feat(web): scaffold Next.js 16 dashboard with design system and auth client (#82)

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

apps/web/src/components/layout/topbar.tsx

@@ -0,0 +1,32 @@
+'use client';
+
+import { useSession, signOut } from '@/lib/auth-client';
+
+export function Topbar(): React.ReactElement {
+  const { data: session } = useSession();
+
+  return (
+    <header className="sticky top-0 z-20 flex h-14 items-center justify-between border-b border-surface-border bg-surface-card/80 px-6 backdrop-blur-sm">
+      <div />
+
+      <div className="flex items-center gap-4">
+        {session?.user ? (
+          <>
+            <span className="text-sm text-text-secondary">
+              {session.user.name ?? session.user.email}
+            </span>
+            <button
+              type="button"
+              onClick={() => signOut()}
+              className="rounded-md px-3 py-1.5 text-sm text-text-muted transition-colors hover:bg-surface-elevated hover:text-text-primary"
+            >
+              Sign out
+            </button>
+          </>
+        ) : (
+          <span className="text-sm text-text-muted">Not signed in</span>
+        )}
+      </div>
+    </header>
+  );
+}