feat(web): add sidebar nav layout and dashboard home page

apps/web/app/page.tsx

@@ -1,8 +1,26 @@
+import Link from 'next/link';
+
 export default function Home() {
   return (
-    <main className="flex min-h-screen flex-col items-center justify-center gap-4">
-      <h1 className="text-4xl font-bold tracking-tight">Insignia TOWER</h1>
-      <p className="text-lg text-gray-500">Community Knowledge Infrastructure Platform</p>
-    </main>
+    <div className="flex flex-col gap-6 max-w-xl">
+      <h1 className="text-3xl font-bold tracking-tight">Insignia TOWER</h1>
+      <p className="text-gray-500">Community Knowledge Infrastructure Platform</p>
+      <div className="flex gap-4">
+        <Link
+          href="/search"
+          className="flex-1 rounded-xl border border-gray-200 bg-white p-5 hover:border-blue-400 transition-colors"
+        >
+          <h2 className="font-semibold mb-1">Search</h2>
+          <p className="text-sm text-gray-500">Full-text search of approved messages</p>
+        </Link>
+        <Link
+          href="/groups"
+          className="flex-1 rounded-xl border border-gray-200 bg-white p-5 hover:border-blue-400 transition-colors"
+        >
+          <h2 className="font-semibold mb-1">Groups</h2>
+          <p className="text-sm text-gray-500">Manage groups and sync routes</p>
+        </Link>
+      </div>
+    </div>
   );
 }