feat(web): add error boundaries, 404 page, loading states, and SEO metadata

- Add branded not-found.tsx with navigation links
- Add global error.tsx boundary with retry and error digest display
- Add root loading.tsx skeleton for route transitions
- Expand root layout metadata: OpenGraph, Twitter cards, robots, viewport
- Add sitemap.ts and robots.ts for SEO
- Add search page and listing detail metadata via route layouts

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/app/(dashboard)/listings/[id]/layout.tsx

@@ -0,0 +1,10 @@
+import type { Metadata } from 'next';
+
+export const metadata: Metadata = {
+  title: 'Chi tiết tin đăng',
+  description: 'Xem chi tiết bất động sản trên GoodGo.',
+};
+
+export default function ListingDetailLayout({ children }: { children: React.ReactNode }) {
+  return children;
+}