feat: Add comprehensive SEO implementation

- Add robots.txt with admin/API blocking
- Add dynamic sitemap.xml with static pages and genre pages
- Implement full meta tags (Open Graph, Twitter Cards, Canonical, Alternates)
- Add SEO helper functions for domain detection and URL generation
- Add generateMetadata to all pages (homepage, about, genre, special)
- Support automatic domain detection for hoerdle.de and hördle.de
- Add SEO configuration to lib/config.ts

lib/config.ts

@@ -12,5 +12,9 @@ export const config = {
         text: process.env.NEXT_PUBLIC_CREDITS_TEXT || 'Vibe coded with ☕ and 🍺 by',
         linkText: process.env.NEXT_PUBLIC_CREDITS_LINK_TEXT || '@elpatron@digitalcourage.social',
         linkUrl: process.env.NEXT_PUBLIC_CREDITS_LINK_URL || 'https://digitalcourage.social/@elpatron',
+    },
+    seo: {
+        ogImage: process.env.NEXT_PUBLIC_OG_IMAGE || '/favicon.ico',
+        twitterHandle: process.env.NEXT_PUBLIC_TWITTER_HANDLE || undefined,
     }
 };