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/api/src/app.module.ts

@@ -46,6 +46,11 @@ import { AppController } from './app.controller';
           ttl: 60_000,
           limit: 10,
         },
+        {
+          name: 'payment-callback',
+          ttl: 60_000,
+          limit: 20,
+        },
       ],
     }),
   ],