diff --git a/apps/web/src/app/(authenticated)/layout.tsx b/apps/web/src/app/(authenticated)/layout.tsx
index 2580c03..0be3a61 100644
--- a/apps/web/src/app/(authenticated)/layout.tsx
+++ b/apps/web/src/app/(authenticated)/layout.tsx
@@ -4,8 +4,10 @@ import { useEffect } from "react";
 import { useRouter } from "next/navigation";
 import { useAuth } from "@/lib/auth/auth-context";
 import { IS_MOCK_AUTH_MODE } from "@/lib/config";
-import { Navigation } from "@/components/layout/Navigation";
+import { AppHeader } from "@/components/layout/AppHeader";
+import { AppSidebar } from "@/components/layout/AppSidebar";
 import { ChatOverlay } from "@/components/chat";
+import { MosaicSpinner } from "@/components/ui/MosaicSpinner";
 import type { ReactNode } from "react";
 
 export default function AuthenticatedLayout({
@@ -23,11 +25,7 @@ export default function AuthenticatedLayout({
   }, [isAuthenticated, isLoading, router]);
 
   if (isLoading) {
-    return (
-      <div className="flex min-h-screen items-center justify-center">
-        <div className="animate-spin rounded-full h-12 w-12 border-b-2 border-gray-900"></div>
-      </div>
-    );
+    return <MosaicSpinner size={48} fullPage />;
   }
 
   if (!isAuthenticated) {
@@ -35,19 +33,31 @@ export default function AuthenticatedLayout({
   }
 
   return (
-    <div className="min-h-screen bg-gray-50">
-      <Navigation />
-      <div className="pt-16">
+    <div className="app-shell">
+      {/* Full-width header — grid-column: 1 / -1 via .app-header CSS class */}
+      <AppHeader />
+
+      {/* Sidebar — left column, row 2, via .app-sidebar CSS class */}
+      <AppSidebar />
+
+      {/* Main content — right column, row 2, via .app-main CSS class */}
+      <main className="app-main" id="main-content">
         {IS_MOCK_AUTH_MODE && (
           <div
-            className="border-b border-amber-300 bg-amber-50 px-4 py-2 text-sm text-amber-900"
+            className="border-b px-4 py-2 text-xs font-medium flex-shrink-0"
+            style={{
+              borderColor: "var(--ms-amber-500)",
+              background: "rgba(245, 158, 11, 0.08)",
+              color: "var(--ms-amber-400)",
+            }}
             data-testid="mock-auth-banner"
           >
             Mock Auth Mode (Local Only): Real authentication is bypassed for frontend development.
           </div>
         )}
-        {children}
-      </div>
+        <div className="flex-1 overflow-y-auto p-5">{children}</div>
+      </main>
+
       {!IS_MOCK_AUTH_MODE && <ChatOverlay />}
     </div>
   );
diff --git a/apps/web/src/app/globals.css b/apps/web/src/app/globals.css
index a7bdc88..9206789 100644
--- a/apps/web/src/app/globals.css
+++ b/apps/web/src/app/globals.css
@@ -3,147 +3,250 @@
 @tailwind utilities;
 
 /* =============================================================================
-   DESIGN C: PROFESSIONAL/ENTERPRISE DESIGN SYSTEM
-   Philosophy: "Good design is as little design as possible." - Dieter Rams
+   MOSAIC DESIGN SYSTEM — Reference token system from dashboard design
    ============================================================================= */
 
 /* -----------------------------------------------------------------------------
-   CSS Custom Properties - Light Theme (Default)
+   Primitive Tokens (Dark-first — dark is the default theme)
    ----------------------------------------------------------------------------- */
 :root {
-  /* Base colors - increased contrast from surfaces */
-  --color-background: 245 247 250;
-  --color-foreground: 15 23 42;
+  /* Mosaic design tokens — dark palette (default) */
+  --ms-bg-950: #080b12;
+  --ms-bg-900: #0f141d;
+  --ms-bg-850: #151b26;
+  --ms-surface-800: #1b2331;
+  --ms-surface-750: #232d3f;
+  --ms-border-700: #2f3b52;
+  --ms-text-100: #eef3ff;
+  --ms-text-300: #c5d0e6;
+  --ms-text-500: #8f9db7;
+  --ms-blue-500: #2f80ff;
+  --ms-blue-400: #56a0ff;
+  --ms-red-500: #e5484d;
+  --ms-red-400: #f06a6f;
+  --ms-purple-500: #8b5cf6;
+  --ms-purple-400: #a78bfa;
+  --ms-teal-500: #14b8a6;
+  --ms-teal-400: #2dd4bf;
+  --ms-amber-500: #f59e0b;
+  --ms-amber-400: #fbbf24;
+  --ms-pink-500: #ec4899;
+  --ms-emerald-500: #10b981;
+  --ms-orange-500: #f97316;
+  --ms-cyan-500: #06b6d4;
+  --ms-indigo-500: #6366f1;
 
-  /* Surface hierarchy (elevation levels) - improved contrast */
-  --surface-0: 255 255 255;
-  --surface-1: 250 251 252;
-  --surface-2: 241 245 249;
-  --surface-3: 226 232 240;
+  /* Semantic aliases — dark theme is default */
+  --bg: var(--ms-bg-900);
+  --bg-deep: var(--ms-bg-950);
+  --bg-mid: var(--ms-bg-850);
+  --surface: var(--ms-surface-800);
+  --surface-2: var(--ms-surface-750);
+  --border: var(--ms-border-700);
+  --text: var(--ms-text-100);
+  --text-2: var(--ms-text-300);
+  --muted: var(--ms-text-500);
+  --primary: var(--ms-blue-500);
+  --primary-l: var(--ms-blue-400);
+  --danger: var(--ms-red-500);
+  --success: var(--ms-teal-500);
+  --warn: var(--ms-amber-500);
+  --purple: var(--ms-purple-500);
 
-  /* Text hierarchy */
-  --text-primary: 15 23 42;
-  --text-secondary: 51 65 85;
-  --text-tertiary: 71 85 105;
-  --text-muted: 100 116 139;
+  /* Typography */
+  --font: var(--font-outfit, 'Outfit'), system-ui, sans-serif;
+  --mono: var(--font-fira-code, 'Fira Code'), 'Cascadia Code', monospace;
 
-  /* Border colors - stronger borders for light mode */
-  --border-default: 203 213 225;
-  --border-subtle: 226 232 240;
-  --border-strong: 148 163 184;
+  /* Radius scale */
+  --r: 8px;
+  --r-sm: 5px;
+  --r-lg: 12px;
+  --r-xl: 16px;
 
-  /* Brand accent - Indigo (professional, trustworthy) */
-  --accent-primary: 79 70 229;
-  --accent-primary-hover: 67 56 202;
-  --accent-primary-light: 238 242 255;
-  --accent-primary-muted: 199 210 254;
+  /* Layout dimensions */
+  --sidebar-w: 260px;
+  --topbar-h: 56px;
+  --terminal-h: 220px;
 
-  /* Semantic colors - Success (Emerald) */
-  --semantic-success: 16 185 129;
-  --semantic-success-light: 209 250 229;
-  --semantic-success-dark: 6 95 70;
+  /* Easing */
+  --ease: cubic-bezier(0.16, 1, 0.3, 1);
 
-  /* Semantic colors - Warning (Amber) */
-  --semantic-warning: 245 158 11;
-  --semantic-warning-light: 254 243 199;
-  --semantic-warning-dark: 146 64 14;
-
-  /* Semantic colors - Error (Rose) */
-  --semantic-error: 244 63 94;
-  --semantic-error-light: 255 228 230;
-  --semantic-error-dark: 159 18 57;
-
-  /* Semantic colors - Info (Sky) */
-  --semantic-info: 14 165 233;
-  --semantic-info-light: 224 242 254;
-  --semantic-info-dark: 3 105 161;
-
-  /* Focus ring */
-  --focus-ring: 99 102 241;
-  --focus-ring-offset: 255 255 255;
-
-  /* Shadows - visible but subtle */
-  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05), 0 1px 3px 0 rgb(0 0 0 / 0.05);
-  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.08), 0 2px 4px -2px rgb(0 0 0 / 0.06);
-  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.08);
-}
-
-/* -----------------------------------------------------------------------------
-   CSS Custom Properties - Dark Theme
-   ----------------------------------------------------------------------------- */
-.dark {
-  --color-background: 3 7 18;
-  --color-foreground: 248 250 252;
-
-  /* Surface hierarchy (elevation levels) */
-  --surface-0: 15 23 42;
-  --surface-1: 30 41 59;
-  --surface-2: 51 65 85;
-  --surface-3: 71 85 105;
-
-  /* Text hierarchy */
-  --text-primary: 248 250 252;
-  --text-secondary: 203 213 225;
-  --text-tertiary: 148 163 184;
-  --text-muted: 100 116 139;
-
-  /* Border colors */
-  --border-default: 51 65 85;
-  --border-subtle: 30 41 59;
-  --border-strong: 71 85 105;
-
-  /* Brand accent adjustments for dark mode */
-  --accent-primary: 129 140 248;
-  --accent-primary-hover: 165 180 252;
-  --accent-primary-light: 30 27 75;
-  --accent-primary-muted: 55 48 163;
-
-  /* Semantic colors adjustments */
-  --semantic-success: 52 211 153;
-  --semantic-success-light: 6 78 59;
-  --semantic-success-dark: 167 243 208;
-
-  --semantic-warning: 251 191 36;
-  --semantic-warning-light: 120 53 15;
-  --semantic-warning-dark: 253 230 138;
-
-  --semantic-error: 251 113 133;
-  --semantic-error-light: 136 19 55;
-  --semantic-error-dark: 253 164 175;
-
-  --semantic-info: 56 189 248;
-  --semantic-info-light: 12 74 110;
-  --semantic-info-dark: 186 230 253;
-
-  /* Focus ring */
-  --focus-ring: 129 140 248;
-  --focus-ring-offset: 15 23 42;
-
-  /* Shadows - subtle glow in dark mode */
+  /* Legacy shadow tokens (retained for component compat) */
   --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.3);
   --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.4), 0 2px 4px -2px rgb(0 0 0 / 0.3);
   --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.5), 0 4px 6px -4px rgb(0 0 0 / 0.4);
 }
 
+/* -----------------------------------------------------------------------------
+   Light Theme Override — applied via data-theme attribute on <html>
+   ----------------------------------------------------------------------------- */
+[data-theme="light"] {
+  --ms-bg-950: #f8faff;
+  --ms-bg-900: #f0f4fc;
+  --ms-bg-850: #e8edf8;
+  --ms-surface-800: #dde4f2;
+  --ms-surface-750: #d0d9ec;
+  --ms-border-700: #b8c4de;
+  --ms-text-100: #0f141d;
+  --ms-text-300: #2f3b52;
+  --ms-text-500: #5a6a87;
+
+  /* Re-alias semantics for light — identical structure, primitive tokens differ */
+  --bg: var(--ms-bg-900);
+  --bg-deep: var(--ms-bg-950);
+  --bg-mid: var(--ms-bg-850);
+  --surface: var(--ms-surface-800);
+  --surface-2: var(--ms-surface-750);
+  --border: var(--ms-border-700);
+  --text: var(--ms-text-100);
+  --text-2: var(--ms-text-300);
+  --muted: var(--ms-text-500);
+
+  /* Lighter shadows for light mode */
+  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05), 0 1px 3px 0 rgb(0 0 0 / 0.05);
+  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.08), 0 2px 4px -2px rgb(0 0 0 / 0.06);
+  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.08);
+}
+
 /* -----------------------------------------------------------------------------
    Base Styles
    ----------------------------------------------------------------------------- */
-* {
+*,
+*::before,
+*::after {
   box-sizing: border-box;
 }
 
 html {
+  font-size: 15px;
   font-feature-settings: "cv02", "cv03", "cv04", "cv11";
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;
 }
 
 body {
-  color: rgb(var(--text-primary));
-  background: rgb(var(--color-background));
-  font-size: 14px;
+  font-family: var(--font);
+  background: var(--bg);
+  color: var(--text);
   line-height: 1.5;
-  transition: background-color 0.15s ease, color 0.15s ease;
+}
+
+a {
+  color: inherit;
+  text-decoration: none;
+}
+
+button {
+  font-family: inherit;
+  cursor: pointer;
+  border: none;
+  background: none;
+  color: inherit;
+}
+
+input,
+select,
+textarea {
+  font-family: inherit;
+}
+
+ul {
+  list-style: none;
+}
+
+/* Subtle grain/noise overlay for texture */
+body::before {
+  content: '';
+  position: fixed;
+  inset: 0;
+  pointer-events: none;
+  z-index: 9999;
+  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)' opacity='1'/%3E%3C/svg%3E");
+  opacity: 0.025;
+}
+
+/* -----------------------------------------------------------------------------
+   Focus States - Accessible & Visible
+   ----------------------------------------------------------------------------- */
+@layer base {
+  :focus-visible {
+    outline: 2px solid var(--ms-blue-400);
+    outline-offset: 2px;
+  }
+
+  :focus:not(:focus-visible) {
+    outline: none;
+  }
+}
+
+/* -----------------------------------------------------------------------------
+   Scrollbar Styling - Minimal & Professional
+   ----------------------------------------------------------------------------- */
+::-webkit-scrollbar {
+  width: 6px;
+  height: 6px;
+}
+
+::-webkit-scrollbar-track {
+  background: transparent;
+}
+
+::-webkit-scrollbar-thumb {
+  background: var(--border);
+  border-radius: 3px;
+}
+
+::-webkit-scrollbar-thumb:hover {
+  background: var(--muted);
+}
+
+/* Firefox */
+* {
+  scrollbar-width: thin;
+  scrollbar-color: var(--border) transparent;
+}
+
+/* -----------------------------------------------------------------------------
+   App Shell Grid Layout
+   ----------------------------------------------------------------------------- */
+.app-shell {
+  display: grid;
+  grid-template-columns: var(--sidebar-w) 1fr;
+  grid-template-rows: var(--topbar-h) 1fr;
+  height: 100vh;
+  overflow: hidden;
+}
+
+.app-header {
+  grid-column: 1 / -1;
+  grid-row: 1;
+  background: var(--bg-deep);
+  border-bottom: 1px solid var(--border);
+  display: flex;
+  align-items: center;
+  padding: 0 20px;
+  gap: 12px;
+  z-index: 100;
+}
+
+.app-sidebar {
+  grid-column: 1;
+  grid-row: 2;
+  background: var(--bg-deep);
+  border-right: 1px solid var(--border);
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+}
+
+.app-main {
+  grid-column: 2;
+  grid-row: 2;
+  background: var(--bg);
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+  position: relative;
 }
 
 /* -----------------------------------------------------------------------------
@@ -182,102 +285,10 @@ body {
   }
 
   .text-mono {
-    font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
+    font-family: var(--mono);
     font-size: 0.8125rem;
     line-height: 1.25rem;
   }
-
-  /* Text color utilities */
-  .text-primary {
-    color: rgb(var(--text-primary));
-  }
-
-  .text-secondary {
-    color: rgb(var(--text-secondary));
-  }
-
-  .text-tertiary {
-    color: rgb(var(--text-tertiary));
-  }
-
-  .text-muted {
-    color: rgb(var(--text-muted));
-  }
-}
-
-/* -----------------------------------------------------------------------------
-   Surface & Card Utilities
-   ----------------------------------------------------------------------------- */
-@layer utilities {
-  .surface-0 {
-    background-color: rgb(var(--surface-0));
-  }
-
-  .surface-1 {
-    background-color: rgb(var(--surface-1));
-  }
-
-  .surface-2 {
-    background-color: rgb(var(--surface-2));
-  }
-
-  .surface-3 {
-    background-color: rgb(var(--surface-3));
-  }
-
-  .border-default {
-    border-color: rgb(var(--border-default));
-  }
-
-  .border-subtle {
-    border-color: rgb(var(--border-subtle));
-  }
-
-  .border-strong {
-    border-color: rgb(var(--border-strong));
-  }
-}
-
-/* -----------------------------------------------------------------------------
-   Focus States - Accessible & Visible
-   ----------------------------------------------------------------------------- */
-@layer base {
-  :focus-visible {
-    outline: 2px solid rgb(var(--focus-ring));
-    outline-offset: 2px;
-  }
-
-  /* Remove default focus for mouse users */
-  :focus:not(:focus-visible) {
-    outline: none;
-  }
-}
-
-/* -----------------------------------------------------------------------------
-   Scrollbar Styling - Minimal & Professional
-   ----------------------------------------------------------------------------- */
-::-webkit-scrollbar {
-  width: 6px;
-  height: 6px;
-}
-
-::-webkit-scrollbar-track {
-  background: transparent;
-}
-
-::-webkit-scrollbar-thumb {
-  background: rgb(var(--text-muted) / 0.4);
-  border-radius: 3px;
-}
-
-::-webkit-scrollbar-thumb:hover {
-  background: rgb(var(--text-muted) / 0.6);
-}
-
-/* Firefox */
-* {
-  scrollbar-width: thin;
-  scrollbar-color: rgb(var(--text-muted) / 0.4) transparent;
 }
 
 /* -----------------------------------------------------------------------------
@@ -292,40 +303,46 @@ body {
 
   .btn-primary {
     @apply btn px-4 py-2;
-    background-color: rgb(var(--accent-primary));
+    background: linear-gradient(135deg, var(--ms-blue-500), var(--ms-purple-500));
     color: white;
+    border-radius: var(--r);
   }
 
   .btn-primary:hover:not(:disabled) {
-    background-color: rgb(var(--accent-primary-hover));
+    box-shadow: 0 8px 28px rgba(47, 128, 255, 0.38);
+    transform: translateY(-1px);
   }
 
   .btn-secondary {
     @apply btn px-4 py-2;
-    background-color: rgb(var(--surface-2));
-    color: rgb(var(--text-primary));
-    border: 1px solid rgb(var(--border-default));
+    background-color: var(--surface);
+    color: var(--text-2);
+    border: 1px solid var(--border);
+    border-radius: var(--r);
   }
 
   .btn-secondary:hover:not(:disabled) {
-    background-color: rgb(var(--surface-3));
+    background-color: var(--surface-2);
+    color: var(--text);
   }
 
   .btn-ghost {
     @apply btn px-3 py-2;
     background-color: transparent;
-    color: rgb(var(--text-secondary));
+    color: var(--muted);
+    border-radius: var(--r);
   }
 
   .btn-ghost:hover:not(:disabled) {
-    background-color: rgb(var(--surface-2));
-    color: rgb(var(--text-primary));
+    background-color: var(--surface);
+    color: var(--text);
   }
 
   .btn-danger {
     @apply btn px-4 py-2;
-    background-color: rgb(var(--semantic-error));
+    background-color: var(--danger);
     color: white;
+    border-radius: var(--r);
   }
 
   .btn-danger:hover:not(:disabled) {
@@ -346,34 +363,36 @@ body {
    ----------------------------------------------------------------------------- */
 @layer components {
   .input {
-    @apply w-full rounded-md px-3 py-2 text-sm transition-all duration-150;
-    @apply focus:outline-none focus:ring-2 focus:ring-offset-0;
-    background-color: rgb(var(--surface-0));
-    border: 1px solid rgb(var(--border-default));
-    color: rgb(var(--text-primary));
+    @apply w-full text-sm transition-all duration-150;
+    @apply focus:outline-none;
+    background-color: var(--bg);
+    border: 1px solid var(--border);
+    border-radius: var(--r);
+    color: var(--text);
+    padding: 11px 14px;
   }
 
   .input::placeholder {
-    color: rgb(var(--text-muted));
+    color: var(--muted);
   }
 
   .input:focus {
-    border-color: rgb(var(--accent-primary));
-    box-shadow: 0 0 0 3px rgb(var(--accent-primary) / 0.1);
+    border-color: var(--primary);
+    box-shadow: 0 0 0 3px rgba(47, 128, 255, 0.12);
   }
 
   .input:disabled {
     @apply opacity-50 cursor-not-allowed;
-    background-color: rgb(var(--surface-1));
+    background-color: var(--surface);
   }
 
   .input-error {
-    border-color: rgb(var(--semantic-error));
+    border-color: var(--danger);
   }
 
   .input-error:focus {
-    border-color: rgb(var(--semantic-error));
-    box-shadow: 0 0 0 3px rgb(var(--semantic-error) / 0.1);
+    border-color: var(--danger);
+    box-shadow: 0 0 0 3px rgba(229, 72, 77, 0.12);
   }
 }
 
@@ -383,8 +402,8 @@ body {
 @layer components {
   .card {
     @apply rounded-lg p-4;
-    background-color: rgb(var(--surface-0));
-    border: 1px solid rgb(var(--border-default));
+    background-color: var(--surface);
+    border: 1px solid var(--border);
     box-shadow: var(--shadow-sm);
   }
 
@@ -398,7 +417,7 @@ body {
   }
 
   .card-interactive:hover {
-    border-color: rgb(var(--border-strong));
+    border-color: var(--muted);
     box-shadow: var(--shadow-md);
   }
 }
@@ -412,33 +431,33 @@ body {
   }
 
   .badge-success {
-    background-color: rgb(var(--semantic-success-light));
-    color: rgb(var(--semantic-success-dark));
+    background-color: rgba(20, 184, 166, 0.15);
+    color: var(--ms-teal-400);
   }
 
   .badge-warning {
-    background-color: rgb(var(--semantic-warning-light));
-    color: rgb(var(--semantic-warning-dark));
+    background-color: rgba(245, 158, 11, 0.15);
+    color: var(--ms-amber-400);
   }
 
   .badge-error {
-    background-color: rgb(var(--semantic-error-light));
-    color: rgb(var(--semantic-error-dark));
+    background-color: rgba(229, 72, 77, 0.15);
+    color: var(--ms-red-400);
   }
 
   .badge-info {
-    background-color: rgb(var(--semantic-info-light));
-    color: rgb(var(--semantic-info-dark));
+    background-color: rgba(47, 128, 255, 0.15);
+    color: var(--ms-blue-400);
   }
 
   .badge-neutral {
-    background-color: rgb(var(--surface-2));
-    color: rgb(var(--text-secondary));
+    background-color: var(--surface-2);
+    color: var(--text-2);
   }
 
   .badge-primary {
-    background-color: rgb(var(--accent-primary-light));
-    color: rgb(var(--accent-primary));
+    background-color: rgba(47, 128, 255, 0.15);
+    color: var(--primary-l);
   }
 }
 
@@ -451,26 +470,29 @@ body {
   }
 
   .status-dot-success {
-    background-color: rgb(var(--semantic-success));
+    background-color: var(--success);
+    box-shadow: 0 0 5px var(--success);
   }
 
   .status-dot-warning {
-    background-color: rgb(var(--semantic-warning));
+    background-color: var(--warn);
+    box-shadow: 0 0 5px var(--warn);
   }
 
   .status-dot-error {
-    background-color: rgb(var(--semantic-error));
+    background-color: var(--danger);
+    box-shadow: 0 0 5px var(--danger);
   }
 
   .status-dot-info {
-    background-color: rgb(var(--semantic-info));
+    background-color: var(--primary);
+    box-shadow: 0 0 5px var(--primary);
   }
 
   .status-dot-neutral {
-    background-color: rgb(var(--text-muted));
+    background-color: var(--muted);
   }
 
-  /* Pulsing indicator for live/active status */
   .status-dot-pulse {
     @apply relative;
   }
@@ -489,12 +511,12 @@ body {
 @layer components {
   .kbd {
     @apply inline-flex items-center justify-center rounded px-1.5 py-0.5 text-xs font-medium;
-    background-color: rgb(var(--surface-2));
-    border: 1px solid rgb(var(--border-default));
-    color: rgb(var(--text-tertiary));
-    font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
+    background-color: var(--surface-2);
+    border: 1px solid var(--border);
+    color: var(--muted);
+    font-family: var(--mono);
     min-width: 1.5rem;
-    box-shadow: 0 1px 0 rgb(var(--border-strong));
+    box-shadow: 0 1px 0 var(--border);
   }
 
   .kbd-group {
@@ -512,13 +534,13 @@ body {
 
   .table-pro thead {
     @apply sticky top-0;
-    background-color: rgb(var(--surface-1));
-    border-bottom: 1px solid rgb(var(--border-default));
+    background-color: var(--surface);
+    border-bottom: 1px solid var(--border);
   }
 
   .table-pro th {
     @apply px-4 py-3 text-left text-xs font-semibold uppercase tracking-wider;
-    color: rgb(var(--text-tertiary));
+    color: var(--muted);
   }
 
   .table-pro th.sortable {
@@ -526,16 +548,16 @@ body {
   }
 
   .table-pro th.sortable:hover {
-    color: rgb(var(--text-primary));
+    color: var(--text);
   }
 
   .table-pro tbody tr {
-    border-bottom: 1px solid rgb(var(--border-subtle));
+    border-bottom: 1px solid var(--border);
     transition: background-color 0.1s ease;
   }
 
   .table-pro tbody tr:hover {
-    background-color: rgb(var(--surface-1));
+    background-color: var(--surface);
   }
 
   .table-pro td {
@@ -555,9 +577,9 @@ body {
     @apply animate-pulse rounded;
     background: linear-gradient(
       90deg,
-      rgb(var(--surface-2)) 0%,
-      rgb(var(--surface-1)) 50%,
-      rgb(var(--surface-2)) 100%
+      var(--surface) 0%,
+      var(--surface-2) 50%,
+      var(--surface) 100%
     );
     background-size: 200% 100%;
   }
@@ -590,15 +612,16 @@ body {
   }
 
   .modal-content {
-    @apply relative max-h-[90vh] w-full max-w-lg overflow-y-auto rounded-lg;
-    background-color: rgb(var(--surface-0));
-    border: 1px solid rgb(var(--border-default));
+    @apply relative max-h-[90vh] w-full max-w-lg overflow-y-auto;
+    background-color: var(--surface);
+    border: 1px solid var(--border);
+    border-radius: var(--r-lg);
     box-shadow: var(--shadow-lg);
   }
 
   .modal-header {
     @apply flex items-center justify-between p-4 border-b;
-    border-color: rgb(var(--border-default));
+    border-color: var(--border);
   }
 
   .modal-body {
@@ -607,7 +630,7 @@ body {
 
   .modal-footer {
     @apply flex items-center justify-end gap-3 p-4 border-t;
-    border-color: rgb(var(--border-default));
+    border-color: var(--border);
   }
 }
 
@@ -617,9 +640,10 @@ body {
 @layer components {
   .tooltip {
     @apply absolute z-50 rounded px-2 py-1 text-xs font-medium;
-    background-color: rgb(var(--text-primary));
-    color: rgb(var(--color-background));
+    background-color: var(--text);
+    color: var(--bg);
     box-shadow: var(--shadow-md);
+    border-radius: var(--r-sm);
   }
 
   .tooltip::before {
@@ -630,7 +654,7 @@ body {
 
   .tooltip-top::before {
     @apply left-1/2 top-full -translate-x-1/2;
-    border-top-color: rgb(var(--text-primary));
+    border-top-color: var(--text);
   }
 }
 
@@ -680,12 +704,10 @@ body {
   animation: scaleIn 0.15s ease-out;
 }
 
-/* Message animation - subtle for chat */
 .message-animate {
   animation: slideIn 0.2s ease-out;
 }
 
-/* Menu dropdown animation */
 .animate-menu-enter {
   animation: scaleIn 0.1s ease-out;
 }
@@ -710,13 +732,8 @@ body {
    ----------------------------------------------------------------------------- */
 @media (prefers-contrast: high) {
   :root {
-    --border-default: 100 116 139;
-    --border-strong: 71 85 105;
-  }
-
-  .dark {
-    --border-default: 148 163 184;
-    --border-strong: 203 213 225;
+    --border: #4a5a78;
+    --muted: #a0b0cc;
   }
 }
 
diff --git a/apps/web/src/app/layout.tsx b/apps/web/src/app/layout.tsx
index bd9a6c4..90c96bc 100644
--- a/apps/web/src/app/layout.tsx
+++ b/apps/web/src/app/layout.tsx
@@ -1,5 +1,6 @@
 import type { Metadata } from "next";
 import type { ReactNode } from "react";
+import { Outfit, Fira_Code } from "next/font/google";
 import { AuthProvider } from "@/lib/auth/auth-context";
 import { ErrorBoundary } from "@/components/error-boundary";
 import { ThemeProvider } from "@/providers/ThemeProvider";
@@ -12,6 +13,18 @@ export const metadata: Metadata = {
   description: "Mosaic Stack Web Application",
 };
 
+const outfit = Outfit({
+  subsets: ["latin"],
+  variable: "--font-outfit",
+  display: "swap",
+});
+
+const firaCode = Fira_Code({
+  subsets: ["latin"],
+  variable: "--font-fira-code",
+  display: "swap",
+});
+
 /**
  * Runtime env vars injected as a synchronous script so client-side modules
  * can read them before React hydration.  This allows Docker env vars to
@@ -34,7 +47,7 @@ function runtimeEnvScript(): string {
 
 export default function RootLayout({ children }: { children: ReactNode }): React.JSX.Element {
   return (
-    <html lang="en">
+    <html lang="en" className={`${outfit.variable} ${firaCode.variable}`}>
       <head>
         <script dangerouslySetInnerHTML={{ __html: runtimeEnvScript() }} />
       </head>
diff --git a/apps/web/src/components/layout/AppHeader.tsx b/apps/web/src/components/layout/AppHeader.tsx
new file mode 100644
index 0000000..6164bca
--- /dev/null
+++ b/apps/web/src/components/layout/AppHeader.tsx
@@ -0,0 +1,114 @@
+"use client";
+
+import Link from "next/link";
+import { useAuth } from "@/lib/auth/auth-context";
+import { LogoutButton } from "@/components/auth/LogoutButton";
+import { ThemeToggle } from "./ThemeToggle";
+
+/**
+ * Full-width application header (topbar).
+ * Logo/brand MUST live here — not in the sidebar — per MS15 design spec.
+ * Spans grid-column 1 / -1 in the app shell grid layout.
+ */
+export function AppHeader(): React.JSX.Element {
+  const { user } = useAuth();
+
+  return (
+    <header className="app-header">
+      {/* Brand / Logo — full-width header, left-anchored */}
+      <Link
+        href="/"
+        className="flex items-center gap-2 flex-shrink-0"
+        aria-label="Mosaic Stack home"
+      >
+        {/* Mosaic logo mark: four colored squares + center dot */}
+        <div
+          className="relative flex-shrink-0"
+          style={{ width: 28, height: 28 }}
+          aria-hidden="true"
+        >
+          <span
+            className="absolute rounded-sm"
+            style={{
+              top: 0,
+              left: 0,
+              width: 11,
+              height: 11,
+              background: "var(--ms-blue-500)",
+            }}
+          />
+          <span
+            className="absolute rounded-sm"
+            style={{
+              top: 0,
+              right: 0,
+              width: 11,
+              height: 11,
+              background: "var(--ms-purple-500)",
+            }}
+          />
+          <span
+            className="absolute rounded-sm"
+            style={{
+              bottom: 0,
+              right: 0,
+              width: 11,
+              height: 11,
+              background: "var(--ms-teal-500)",
+            }}
+          />
+          <span
+            className="absolute rounded-sm"
+            style={{
+              bottom: 0,
+              left: 0,
+              width: 11,
+              height: 11,
+              background: "var(--ms-amber-500)",
+            }}
+          />
+          <span
+            className="absolute rounded-full"
+            style={{
+              top: "50%",
+              left: "50%",
+              transform: "translate(-50%, -50%)",
+              width: 8,
+              height: 8,
+              background: "var(--ms-pink-500)",
+            }}
+          />
+        </div>
+
+        <span
+          className="text-sm font-bold"
+          style={{
+            background: "linear-gradient(135deg, var(--ms-blue-400), var(--ms-purple-500))",
+            backgroundClip: "text",
+            WebkitBackgroundClip: "text",
+            WebkitTextFillColor: "transparent",
+            letterSpacing: "-0.02em",
+          }}
+        >
+          Mosaic Stack
+        </span>
+      </Link>
+
+      {/* Spacer */}
+      <div className="flex-1" />
+
+      {/* Right side controls */}
+      <div className="flex items-center gap-2">
+        <ThemeToggle />
+
+        {user && (
+          <span className="hidden sm:block text-xs px-2" style={{ color: "var(--muted)" }}>
+            {user.name || user.email}
+          </span>
+        )}
+
+        <LogoutButton variant="secondary" />
+      </div>
+    </header>
+  );
+}
diff --git a/apps/web/src/components/layout/AppSidebar.tsx b/apps/web/src/components/layout/AppSidebar.tsx
new file mode 100644
index 0000000..6f27c8e
--- /dev/null
+++ b/apps/web/src/components/layout/AppSidebar.tsx
@@ -0,0 +1,160 @@
+"use client";
+
+import Link from "next/link";
+import { usePathname } from "next/navigation";
+
+interface NavItem {
+  href: string;
+  label: string;
+  icon: React.JSX.Element;
+}
+
+const navItems: NavItem[] = [
+  {
+    href: "/",
+    label: "Dashboard",
+    icon: (
+      <svg
+        width="16"
+        height="16"
+        viewBox="0 0 24 24"
+        fill="none"
+        stroke="currentColor"
+        strokeWidth="1.5"
+        aria-hidden="true"
+      >
+        <rect x="3" y="3" width="7" height="7" rx="1" />
+        <rect x="14" y="3" width="7" height="7" rx="1" />
+        <rect x="14" y="14" width="7" height="7" rx="1" />
+        <rect x="3" y="14" width="7" height="7" rx="1" />
+      </svg>
+    ),
+  },
+  {
+    href: "/tasks",
+    label: "Tasks",
+    icon: (
+      <svg
+        width="16"
+        height="16"
+        viewBox="0 0 24 24"
+        fill="none"
+        stroke="currentColor"
+        strokeWidth="1.5"
+        aria-hidden="true"
+      >
+        <path d="M9 11l3 3L22 4" />
+        <path d="M21 12v7a2 2 0 01-2 2H5a2 2 0 01-2-2V5a2 2 0 012-2h11" />
+      </svg>
+    ),
+  },
+  {
+    href: "/calendar",
+    label: "Calendar",
+    icon: (
+      <svg
+        width="16"
+        height="16"
+        viewBox="0 0 24 24"
+        fill="none"
+        stroke="currentColor"
+        strokeWidth="1.5"
+        aria-hidden="true"
+      >
+        <rect x="3" y="4" width="18" height="18" rx="2" />
+        <path d="M16 2v4M8 2v4M3 10h18" />
+      </svg>
+    ),
+  },
+  {
+    href: "/knowledge",
+    label: "Knowledge",
+    icon: (
+      <svg
+        width="16"
+        height="16"
+        viewBox="0 0 24 24"
+        fill="none"
+        stroke="currentColor"
+        strokeWidth="1.5"
+        aria-hidden="true"
+      >
+        <path d="M4 19.5A2.5 2.5 0 016.5 17H20" />
+        <path d="M6.5 2H20v20H6.5A2.5 2.5 0 014 19.5v-15A2.5 2.5 0 016.5 2z" />
+      </svg>
+    ),
+  },
+  {
+    href: "/usage",
+    label: "Usage",
+    icon: (
+      <svg
+        width="16"
+        height="16"
+        viewBox="0 0 24 24"
+        fill="none"
+        stroke="currentColor"
+        strokeWidth="1.5"
+        aria-hidden="true"
+      >
+        <path d="M18 20V10M12 20V4M6 20v-6" />
+      </svg>
+    ),
+  },
+];
+
+/**
+ * Application sidebar — navigation only, no brand/logo.
+ * Logo lives in AppHeader per MS15 design spec.
+ */
+export function AppSidebar(): React.JSX.Element {
+  const pathname = usePathname();
+
+  return (
+    <aside className="app-sidebar">
+      {/* Navigation body */}
+      <nav className="flex-1 overflow-y-auto p-2" aria-label="Main navigation">
+        <div className="mb-4 mt-2">
+          <p
+            className="px-2 mb-1 text-xs font-semibold uppercase tracking-widest"
+            style={{ color: "var(--muted)" }}
+          >
+            Navigation
+          </p>
+
+          <ul>
+            {navItems.map((item) => {
+              const isActive = pathname === item.href;
+              return (
+                <li key={item.href}>
+                  <Link
+                    href={item.href}
+                    className="flex items-center gap-3 px-2 py-2 rounded text-sm font-medium transition-colors relative"
+                    style={
+                      isActive
+                        ? { color: "var(--text)", background: "var(--surface)" }
+                        : { color: "var(--muted)" }
+                    }
+                    aria-current={isActive ? "page" : undefined}
+                  >
+                    {isActive && (
+                      <span
+                        className="absolute left-0 top-1.5 bottom-1.5 w-0.5 rounded-r"
+                        style={{ background: "var(--primary)" }}
+                        aria-hidden="true"
+                      />
+                    )}
+                    <span className="flex-shrink-0" style={{ opacity: isActive ? 1 : 0.7 }}>
+                      {item.icon}
+                    </span>
+                    {item.label}
+                  </Link>
+                </li>
+              );
+            })}
+          </ul>
+        </div>
+      </nav>
+    </aside>
+  );
+}
diff --git a/apps/web/src/components/layout/ThemeToggle.tsx b/apps/web/src/components/layout/ThemeToggle.tsx
index a61f148..51281e0 100644
--- a/apps/web/src/components/layout/ThemeToggle.tsx
+++ b/apps/web/src/components/layout/ThemeToggle.tsx
@@ -20,7 +20,7 @@ export function ThemeToggle({ className = "" }: ThemeToggleProps): React.JSX.Ele
         // Sun icon for dark mode (click to switch to light)
         <svg
           className="h-5 w-5"
-          style={{ color: "rgb(var(--semantic-warning))" }}
+          style={{ color: "var(--warn)" }}
           fill="none"
           viewBox="0 0 24 24"
           stroke="currentColor"
@@ -33,7 +33,7 @@ export function ThemeToggle({ className = "" }: ThemeToggleProps): React.JSX.Ele
         // Moon icon for light mode (click to switch to dark)
         <svg
           className="h-5 w-5"
-          style={{ color: "rgb(var(--text-secondary))" }}
+          style={{ color: "var(--text-2)" }}
           fill="none"
           viewBox="0 0 24 24"
           stroke="currentColor"
diff --git a/apps/web/src/components/ui/MosaicLogo.tsx b/apps/web/src/components/ui/MosaicLogo.tsx
new file mode 100644
index 0000000..2b6890e
--- /dev/null
+++ b/apps/web/src/components/ui/MosaicLogo.tsx
@@ -0,0 +1,100 @@
+"use client";
+
+import type { CSSProperties } from "react";
+
+export interface MosaicLogoProps {
+  /** Width and height in pixels (default: 36) */
+  size?: number;
+  /** Whether to animate rotation (default: false) */
+  spinning?: boolean;
+  /** Seconds for one full rotation (default: 20) */
+  spinDuration?: number;
+  /** Additional CSS classes for the root element */
+  className?: string;
+}
+
+/**
+ * MosaicLogo renders the 5-element Mosaic logo icon:
+ * - 4 corner squares (blue, purple, teal, amber)
+ * - 1 center circle (pink)
+ *
+ * Colors use CSS custom properties so they respond to theme changes.
+ * When `spinning` is true the logo rotates continuously, making it
+ * suitable for use as a loading indicator.
+ */
+export function MosaicLogo({
+  size = 36,
+  spinning = false,
+  spinDuration = 20,
+  className = "",
+}: MosaicLogoProps): React.JSX.Element {
+  // Scale factor relative to the 36px reference design
+  const scale = size / 36;
+
+  // Derived dimensions
+  const squareSize = Math.round(14 * scale);
+  const circleSize = Math.round(11 * scale);
+  const borderRadius = Math.round(3 * scale);
+
+  const animationValue = spinning
+    ? `mosaicLogoSpin ${String(spinDuration)}s linear infinite`
+    : undefined;
+
+  const containerStyle: CSSProperties = {
+    width: size,
+    height: size,
+    position: "relative",
+    flexShrink: 0,
+    animation: animationValue,
+    transformOrigin: "center",
+  };
+
+  const baseSquareStyle: CSSProperties = {
+    position: "absolute",
+    width: squareSize,
+    height: squareSize,
+    borderRadius,
+  };
+
+  const circleStyle: CSSProperties = {
+    position: "absolute",
+    top: "50%",
+    left: "50%",
+    transform: "translate(-50%, -50%)",
+    width: circleSize,
+    height: circleSize,
+    borderRadius: "50%",
+    background: "var(--ms-pink-500)",
+  };
+
+  return (
+    <>
+      {spinning && (
+        <style>{`
+          @keyframes mosaicLogoSpin {
+            from { transform: rotate(0deg); }
+            to   { transform: rotate(360deg); }
+          }
+        `}</style>
+      )}
+      <div style={containerStyle} className={className} role="img" aria-label="Mosaic logo">
+        {/* Top-left: blue */}
+        <div style={{ ...baseSquareStyle, top: 0, left: 0, background: "var(--ms-blue-500)" }} />
+        {/* Top-right: purple */}
+        <div style={{ ...baseSquareStyle, top: 0, right: 0, background: "var(--ms-purple-500)" }} />
+        {/* Bottom-right: teal */}
+        <div
+          style={{ ...baseSquareStyle, bottom: 0, right: 0, background: "var(--ms-teal-500)" }}
+        />
+        {/* Bottom-left: amber */}
+        <div
+          style={{ ...baseSquareStyle, bottom: 0, left: 0, background: "var(--ms-amber-500)" }}
+        />
+        {/* Center: pink circle */}
+        <div style={circleStyle} />
+      </div>
+    </>
+  );
+}
+
+export default MosaicLogo;
diff --git a/apps/web/src/components/ui/MosaicSpinner.tsx b/apps/web/src/components/ui/MosaicSpinner.tsx
new file mode 100644
index 0000000..92af7ef
--- /dev/null
+++ b/apps/web/src/components/ui/MosaicSpinner.tsx
@@ -0,0 +1,49 @@
+"use client";
+
+import { MosaicLogo } from "./MosaicLogo";
+import type { ReactElement } from "react";
+
+export interface MosaicSpinnerProps {
+  /** Width and height of the logo in pixels (default: 36) */
+  size?: number;
+  /** Seconds for one full rotation (default: 20) */
+  spinDuration?: number;
+  /** Optional text label displayed below the spinner */
+  label?: string;
+  /**
+   * When true, wraps the spinner in a full-page centered overlay.
+   * When false (default), renders inline.
+   */
+  fullPage?: boolean;
+  /** Additional CSS classes for the wrapper element */
+  className?: string;
+}
+
+/**
+ * MosaicSpinner wraps MosaicLogo with spinning enabled.
+ * It can be used as a full-page loading overlay or as an inline indicator.
+ */
+export function MosaicSpinner({
+  size = 36,
+  spinDuration = 20,
+  label,
+  fullPage = false,
+  className = "",
+}: MosaicSpinnerProps): ReactElement {
+  const inner = (
+    <div className={`flex flex-col items-center gap-3 ${className}`}>
+      <MosaicLogo size={size} spinning spinDuration={spinDuration} />
+      {label !== undefined && label !== "" && (
+        <span className="text-sm text-gray-500">{label}</span>
+      )}
+    </div>
+  );
+
+  if (fullPage) {
+    return <div className="flex min-h-screen items-center justify-center">{inner}</div>;
+  }
+
+  return inner;
+}
+
+export default MosaicSpinner;
diff --git a/apps/web/src/providers/ThemeProvider.tsx b/apps/web/src/providers/ThemeProvider.tsx
index 623e7fb..a1a68b7 100644
--- a/apps/web/src/providers/ThemeProvider.tsx
+++ b/apps/web/src/providers/ThemeProvider.tsx
@@ -29,6 +29,21 @@ function getStoredTheme(): Theme {
   return "system";
 }
 
+/**
+ * Apply the resolved theme to the <html> element via data-theme attribute.
+ * The default (no attribute or data-theme="dark") renders dark — dark is default.
+ * Light theme requires data-theme="light".
+ */
+function applyThemeAttribute(resolved: "light" | "dark"): void {
+  const root = document.documentElement;
+  if (resolved === "light") {
+    root.setAttribute("data-theme", "light");
+  } else {
+    // Remove the attribute so the default (dark) CSS variables apply.
+    root.removeAttribute("data-theme");
+  }
+}
+
 interface ThemeProviderProps {
   children: ReactNode;
   defaultTheme?: Theme;
@@ -46,19 +61,18 @@ export function ThemeProvider({
   useEffect(() => {
     setMounted(true);
     const storedTheme = getStoredTheme();
+    const resolved = storedTheme === "system" ? getSystemTheme() : storedTheme;
     setThemeState(storedTheme);
-    setResolvedTheme(storedTheme === "system" ? getSystemTheme() : storedTheme);
+    setResolvedTheme(resolved);
+    applyThemeAttribute(resolved);
   }, []);
 
-  // Apply theme class to html element
+  // Apply theme via data-theme attribute on html element
   useEffect(() => {
     if (!mounted) return;
 
-    const root = document.documentElement;
     const resolved = theme === "system" ? getSystemTheme() : theme;
-
-    root.classList.remove("light", "dark");
-    root.classList.add(resolved);
+    applyThemeAttribute(resolved);
     setResolvedTheme(resolved);
   }, [theme, mounted]);
 
@@ -68,9 +82,9 @@ export function ThemeProvider({
 
     const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");
     const handleChange = (e: MediaQueryListEvent): void => {
-      setResolvedTheme(e.matches ? "dark" : "light");
-      document.documentElement.classList.remove("light", "dark");
-      document.documentElement.classList.add(e.matches ? "dark" : "light");
+      const resolved = e.matches ? "dark" : "light";
+      setResolvedTheme(resolved);
+      applyThemeAttribute(resolved);
     };
 
     mediaQuery.addEventListener("change", handleChange);
diff --git a/apps/web/tailwind.config.ts b/apps/web/tailwind.config.ts
index 44a4124..8ab6eb3 100644
--- a/apps/web/tailwind.config.ts
+++ b/apps/web/tailwind.config.ts
@@ -1,10 +1,34 @@
 import type { Config } from "tailwindcss";
 
 const config: Config = {
-  darkMode: "class",
+  // Use data-theme attribute selector for dark mode instead of .dark class
+  darkMode: ["selector", '[data-theme="dark"]'],
   content: ["./src/**/*.{js,ts,jsx,tsx,mdx}", "../../packages/ui/src/**/*.{js,ts,jsx,tsx,mdx}"],
   theme: {
-    extend: {},
+    extend: {
+      fontFamily: {
+        sans: ["var(--font-outfit)", "system-ui", "sans-serif"],
+        mono: ["var(--font-fira-code)", "Cascadia Code", "monospace"],
+      },
+      colors: {
+        // Expose Mosaic semantic tokens as Tailwind colors
+        bg: "var(--bg)",
+        "bg-deep": "var(--bg-deep)",
+        "bg-mid": "var(--bg-mid)",
+        surface: "var(--surface)",
+        "surface-2": "var(--surface-2)",
+        border: "var(--border)",
+        text: "var(--text)",
+        "text-2": "var(--text-2)",
+        muted: "var(--muted)",
+        primary: "var(--primary)",
+        "primary-l": "var(--primary-l)",
+        danger: "var(--danger)",
+        success: "var(--success)",
+        warn: "var(--warn)",
+        purple: "var(--purple)",
+      },
+    },
   },
   plugins: [],
 };
diff --git a/docs/scratchpads/ms15-fe-006-mosaic-logo-spinner.md b/docs/scratchpads/ms15-fe-006-mosaic-logo-spinner.md
new file mode 100644
index 0000000..bfc7461
--- /dev/null
+++ b/docs/scratchpads/ms15-fe-006-mosaic-logo-spinner.md
@@ -0,0 +1,45 @@
+# MS15-FE-006: MosaicLogo and MosaicSpinner Components
+
+## Task
+
+Create Mosaic logo icon component and spinner wrapper for use as the site-wide loading indicator.
+
+## Files to Create
+
+1. `apps/web/src/components/ui/MosaicLogo.tsx` — 5-element logo icon
+2. `apps/web/src/components/ui/MosaicSpinner.tsx` — spinner wrapper
+
+## Files to Modify
+
+1. `apps/web/src/app/(authenticated)/layout.tsx` — replace loading spinner (isLoading block only)
+
+## Design
+
+- 4 corner squares: blue (TL), purple (TR), teal (BR), amber (BL)
+- 1 center circle: pink
+- CSS vars: --ms-blue-500, --ms-purple-500, --ms-teal-500, --ms-amber-500, --ms-pink-500
+- Animation: linear 360deg rotation
+
+## Props
+
+### MosaicLogo
+
+- size?: number (default 36)
+- spinning?: boolean (default false)
+- spinDuration?: number (default 20) seconds
+- className?: string
+
+### MosaicSpinner
+
+- Wraps MosaicLogo with spinning=true
+- label?: string — optional text label below
+- fullPage?: boolean — center on screen
+
+## Status
+
+- [x] Scratchpad created
+- [ ] MosaicLogo.tsx created
+- [ ] MosaicSpinner.tsx created
+- [ ] layout.tsx updated
+- [ ] Lint clean
+- [ ] Committed and pushed