refactor: unify recipe routes into [recipeLang] slug with full bilingual support

Consolidate /rezepte and /recipes routes into single [recipeLang] structure to eliminate code duplication. All pages now use conditional API routing and reactive labels based on language parameter.

- Merge duplicate route structures into /[recipeLang] with 404 for invalid slugs
- Add English API endpoints for search, favorites, tags, and categories
- Implement language dropdown in header with localStorage persistence
- Convert all pages to use Svelte 5 runes (, , )
- Add German-only redirects (301) for add/edit pages
- Make all view pages (list, detail, filters, search, favorites) fully bilingual
- Remove floating language switcher in favor of header dropdown

.env.example

@@ -0,0 +1,28 @@
+# Database Configuration
+MONGO_URL="mongodb://user:password@host:port/database?authSource=admin"
+
+# Authentication Secrets (runtime only - not embedded in build)
+AUTHENTIK_ID="your-authentik-client-id"
+AUTHENTIK_SECRET="your-authentik-client-secret"
+
+# Static Configuration (embedded in build - OK to be public)
+AUTHENTIK_ISSUER="https://sso.example.com/application/o/your-app/"
+
+# File Storage
+IMAGE_DIR="/path/to/static/files"
+
+# Optional: Development Settings
+# DEV_DISABLE_AUTH="true"
+# ORIGIN="http://127.0.0.1:3000"
+
+# Optional: Additional Configuration
+# BEARER_TOKEN="your-bearer-token"
+# COOKIE_SECRET="your-cookie-secret"
+# PEPPER="your-pepper-value"
+# ALLOW_REGISTRATION="1"
+# AUTH_SECRET="your-auth-secret"
+# USDA_API_KEY="your-usda-api-key"
+
+# Translation Service (DeepL API)
+DEEPL_API_KEY="your-deepl-api-key"
+DEEPL_API_URL="https://api-free.deepl.com/v2/translate"  # Use https://api.deepl.com/v2/translate for Pro