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/layout.tsx

@@ -1,10 +1,71 @@
-import type { Metadata } from 'next';
+import type { Metadata, Viewport } from 'next';
 import { AuthProvider } from '@/components/providers/auth-provider';
 import './globals.css';
 
+const siteUrl = process.env['NEXT_PUBLIC_SITE_URL'] || 'https://goodgo.vn';
+
+export const viewport: Viewport = {
+  width: 'device-width',
+  initialScale: 1,
+  themeColor: '#15803d',
+};
+
 export const metadata: Metadata = {
-  title: 'GoodGo Platform',
-  description: 'Vietnam Real Estate Platform',
+  metadataBase: new URL(siteUrl),
+  title: {
+    default: 'GoodGo \u2014 N\u1ec1n t\u1ea3ng B\u1ea5t \u0111\u1ed9ng s\u1ea3n Vi\u1ec7t Nam',
+    template: '%s | GoodGo',
+  },
+  description:
+    'GoodGo \u2014 n\u1ec1n t\u1ea3ng b\u1ea5t \u0111\u1ed9ng s\u1ea3n th\u00f4ng minh t\u1ea1i Vi\u1ec7t Nam. Mua b\u00e1n, cho thu\u00ea nh\u00e0 \u0111\u1ea5t d\u1ec5 d\u00e0ng v\u1edbi h\u01a1n 10,000+ tin \u0111\u0103ng tr\u00ean to\u00e0n qu\u1ed1c.',
+  keywords: [
+    'b\u1ea5t \u0111\u1ed9ng s\u1ea3n',
+    'mua b\u00e1n nh\u00e0 \u0111\u1ea5t',
+    'cho thu\u00ea nh\u00e0',
+    'goodgo',
+    'nh\u00e0 \u0111\u1ea5t vi\u1ec7t nam',
+    'chung c\u01b0',
+    'bi\u1ec7t th\u1ef1',
+    'nh\u00e0 ph\u1ed1',
+    '\u0111\u1ea5t n\u1ec1n',
+  ],
+  authors: [{ name: 'GoodGo' }],
+  creator: 'GoodGo',
+  openGraph: {
+    type: 'website',
+    locale: 'vi_VN',
+    url: siteUrl,
+    siteName: 'GoodGo',
+    title: 'GoodGo \u2014 N\u1ec1n t\u1ea3ng B\u1ea5t \u0111\u1ed9ng s\u1ea3n Vi\u1ec7t Nam',
+    description:
+      'Mua b\u00e1n, cho thu\u00ea b\u1ea5t \u0111\u1ed9ng s\u1ea3n d\u1ec5 d\u00e0ng v\u1edbi GoodGo \u2014 n\u1ec1n t\u1ea3ng th\u00f4ng minh, uy t\u00edn h\u00e0ng \u0111\u1ea7u Vi\u1ec7t Nam.',
+    images: [
+      {
+        url: '/og-image.png',
+        width: 1200,
+        height: 630,
+        alt: 'GoodGo \u2014 N\u1ec1n t\u1ea3ng B\u1ea5t \u0111\u1ed9ng s\u1ea3n Vi\u1ec7t Nam',
+      },
+    ],
+  },
+  twitter: {
+    card: 'summary_large_image',
+    title: 'GoodGo \u2014 N\u1ec1n t\u1ea3ng B\u1ea5t \u0111\u1ed9ng s\u1ea3n Vi\u1ec7t Nam',
+    description:
+      'Mua b\u00e1n, cho thu\u00ea b\u1ea5t \u0111\u1ed9ng s\u1ea3n d\u1ec5 d\u00e0ng v\u1edbi GoodGo.',
+    images: ['/og-image.png'],
+  },
+  robots: {
+    index: true,
+    follow: true,
+    googleBot: {
+      index: true,
+      follow: true,
+      'max-video-preview': -1,
+      'max-image-preview': 'large',
+      'max-snippet': -1,
+    },
+  },
 };
 
 export default function RootLayout({ children }: { children: React.ReactNode }) {