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,
     }
 };

lib/metadata.ts

@@ -0,0 +1,64 @@
+import type { Metadata } from 'next';
+import { config } from './config';
+import { getBaseUrl } from './seo';
+
+/**
+ * Generate base metadata with Open Graph, Twitter Cards, and canonical URLs
+ */
+export async function generateBaseMetadata(
+    locale: string,
+    path: string = '',
+    title?: string,
+    description?: string,
+    image?: string
+): Promise<Metadata> {
+    const baseUrl = await getBaseUrl();
+    const pathSegment = path ? `/${path}` : '';
+    const fullUrl = `${baseUrl}/${locale}${pathSegment}`;
+    
+    // Determine alternate URLs for both locales (same path for both)
+    const alternateLocale = locale === 'de' ? 'en' : 'de';
+    const alternateUrl = `${baseUrl}/${alternateLocale}${pathSegment}`;
+    
+    // Default values
+    const metaTitle = title || config.appName;
+    const metaDescription = description || config.appDescription;
+    const ogImage = image || `${baseUrl}${config.seo.ogImage}`;
+    
+    return {
+        title: metaTitle,
+        description: metaDescription,
+        alternates: {
+            canonical: fullUrl,
+            languages: {
+                [locale]: fullUrl,
+                [alternateLocale]: alternateUrl,
+                'x-default': `${baseUrl}/en${pathSegment}`,
+            },
+        },
+        openGraph: {
+            title: metaTitle,
+            description: metaDescription,
+            url: fullUrl,
+            siteName: config.appName,
+            images: [
+                {
+                    url: ogImage,
+                    width: 1200,
+                    height: 630,
+                    alt: metaTitle,
+                },
+            ],
+            locale: locale,
+            type: 'website',
+        },
+        twitter: {
+            card: 'summary_large_image',
+            title: metaTitle,
+            description: metaDescription,
+            images: [ogImage],
+            ...(config.seo.twitterHandle && { creator: config.seo.twitterHandle }),
+        },
+    };
+}
+

lib/seo.ts

@@ -0,0 +1,43 @@
+import { headers } from 'next/headers';
+import { config } from './config';
+
+/**
+ * Get the current base URL from request headers
+ * Automatically detects hoerdle.de or hördle.de (xn--hrdle-jua.de)
+ */
+export async function getBaseUrl(): Promise<string> {
+    const headersList = await headers();
+    const host = headersList.get('host') || headersList.get('x-forwarded-host') || '';
+    
+    let domain = config.domain; // Default fallback
+    
+    if (host) {
+        // Extract domain from host (remove port if present)
+        const detectedDomain = host.split(':')[0].toLowerCase();
+        
+        // Map domains
+        if (detectedDomain === 'hoerdle.de') {
+            domain = 'hoerdle.de';
+        } else if (detectedDomain === 'hördle.de' || detectedDomain === 'xn--hrdle-jua.de') {
+            domain = 'hördle.de';
+        } else {
+            // Use detected domain if it's different from default
+            domain = detectedDomain;
+        }
+    }
+    
+    // Always use HTTPS in production
+    const protocol = process.env.NODE_ENV === 'production' ? 'https' : 'http';
+    return `${protocol}://${domain}`;
+}
+
+/**
+ * Get base URL synchronously (for use in non-async contexts)
+ * Uses environment variable or config as fallback
+ */
+export function getBaseUrlSync(): string {
+    const domain = process.env.NEXT_PUBLIC_DOMAIN || config.domain;
+    const protocol = process.env.NODE_ENV === 'production' ? 'https' : 'http';
+    return `${protocol}://${domain}`;
+}
+