fix(docker): restore runtime NEXT_PUBLIC vars, add DEFAULT_LOCALE build arg

- Restore NEXT_PUBLIC_SUPABASE_URL + NEXT_PUBLIC_SUPABASE_PUBLIC_KEY at runtime
  (server code reads from process.env — needs these for SSR)
- Use external URL (API_EXTERNAL_URL) for both build and runtime
- Add NEXT_PUBLIC_DEFAULT_LOCALE=de as Dockerfile build arg so next-intl
  compiles with the correct default locale (was falling back to 'en')
- CACHE_BUST=3 to force full rebuild

docker-compose.yml

@@ -321,13 +321,14 @@ services:
     environment:
       NODE_ENV: production
       NEXT_PUBLIC_SITE_URL: ${SITE_URL:-http://localhost:3000}
-      # NEXT_PUBLIC_ vars are baked at build time — runtime values only apply
-      # to middleware/API routes. Don't override with Docker-internal URLs.
+      # Must match the build-time value — server code reads from process.env
+      NEXT_PUBLIC_SUPABASE_URL: ${API_EXTERNAL_URL:-http://localhost:8000}
+      NEXT_PUBLIC_SUPABASE_PUBLIC_KEY: ${SUPABASE_ANON_KEY}
+      NEXT_PUBLIC_DEFAULT_LOCALE: de
       SUPABASE_SECRET_KEY: ${SUPABASE_SERVICE_ROLE_KEY}
       SUPABASE_DB_WEBHOOK_SECRET: ${DB_WEBHOOK_SECRET:-webhooksecret}
       EMAIL_SENDER: ${EMAIL_SENDER:-noreply@myeasycms.de}
       NEXT_PUBLIC_PRODUCT_NAME: MyEasyCMS
-      NEXT_PUBLIC_DEFAULT_LOCALE: de
       NEXT_PUBLIC_ENABLE_THEME_TOGGLE: "true"
       NEXT_PUBLIC_ENABLE_TEAM_ACCOUNTS: "true"
       NEXT_PUBLIC_ENABLE_TEAM_ACCOUNTS_CREATION: "true"