feat(frontend): add react spa with wishlist flows and public profile

apps/frontend/src/pages/NotFoundPage.tsx

@@ -0,0 +1,16 @@
+import { Link } from 'react-router-dom';
+import { Button } from '@/components/ui/Button';
+
+export function NotFoundPage() {
+  return (
+    <div className="flex min-h-screen items-center justify-center p-6">
+      <div className="max-w-md rounded-xl border border-border bg-surface p-8 text-center shadow-card">
+        <h1 className="font-display text-4xl">404</h1>
+        <p className="mt-2 text-muted">We couldn't find that page.</p>
+        <Link to="/" className="mt-4 inline-block">
+          <Button variant="secondary">Back to home</Button>
+        </Link>
+      </div>
+    </div>
+  );
+}