feat(web): add theme selection UI in Settings > Appearance (#495)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/web/src/app/(authenticated)/settings/page.tsx

@@ -95,6 +95,31 @@ function SettingsCategoryCard({ category }: SettingsCategoryCardProps): ReactEle
 }
 
 const categories: CategoryConfig[] = [
+  {
+    title: "Appearance",
+    description:
+      "Choose a theme for the interface. Switch between Dark, Light, Nord, Dracula, and more.",
+    href: "/settings/appearance",
+    accent: "var(--ms-pink-500)",
+    iconBg: "rgba(236, 72, 153, 0.12)",
+    icon: (
+      <svg
+        width="20"
+        height="20"
+        viewBox="0 0 20 20"
+        fill="none"
+        stroke="currentColor"
+        strokeWidth="1.5"
+        strokeLinecap="round"
+        strokeLinejoin="round"
+        aria-hidden="true"
+      >
+        <circle cx="10" cy="10" r="7.5" />
+        <path d="M10 2.5v15" />
+        <path d="M10 2.5a7.5 7.5 0 0 1 0 15" fill="currentColor" opacity="0.15" />
+      </svg>
+    ),
+  },
   {
     title: "Credentials",
     description: