feat: SEO enhancements — server metadata, sitemap, robots, dynamic base URL

- Split all page.tsx files into server wrapper (metadata export) + client.tsx (Apollo/interactive)
- Add robots.ts and sitemap.ts (tournaments, teams, players)
- Add metadataBase, OpenGraph and Twitter card metadata to root layout
- Replace hardcoded worldcup.pivoine.art with NEXT_PUBLIC_SITE_URL env var (sitemap/robots) and relative paths (page metadata, resolved by Next.js against metadataBase)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/layout.tsx

@@ -8,17 +8,31 @@ import { AppApolloProvider } from '@/components/apollo-provider'
 const bebasNeue = Bebas_Neue({ weight: '400', subsets: ['latin'], variable: '--font-bebas' })
 const spaceGrotesk = Space_Grotesk({ subsets: ['latin'], variable: '--font-space' })
 
+const BASE_URL = process.env.NEXT_PUBLIC_SITE_URL ?? 'http://localhost:3000'
+
 export const metadata: Metadata = {
-  title: { default: 'World Cup', template: '%s · World Cup' },
-  description: 'Comprehensive World Cup statistics from 1930 to 2026',
+  metadataBase: new URL(BASE_URL),
+  title: { default: 'World Cup Stats', template: '%s · World Cup' },
+  description: 'Live scores, group standings, results and statistics for every FIFA World Cup from 1930 to 2026.',
+  keywords: ['World Cup', 'FIFA', 'football', 'soccer', 'statistics', 'live scores', 'standings', '2026'],
+  openGraph: {
+    type: 'website',
+    siteName: 'World Cup Stats',
+    url: '/',
+    title: 'World Cup Stats',
+    description: 'Live scores, group standings, results and statistics for every FIFA World Cup from 1930 to 2026.',
+  },
+  twitter: {
+    card: 'summary',
+    title: 'World Cup Stats',
+    description: 'Live scores, group standings, results and statistics for every FIFA World Cup from 1930 to 2026.',
+  },
   icons: {
     icon: [
       { url: '/favicon.svg', type: 'image/svg+xml' },
       { url: '/favicon-32x32.png', sizes: '32x32', type: 'image/png' },
     ],
-    apple: [
-      { url: '/apple-touch-icon.png', sizes: '180x180', type: 'image/png' },
-    ],
+    apple: [{ url: '/apple-touch-icon.png', sizes: '180x180', type: 'image/png' }],
   },
 }