fix(auth): revert SUPABASE_INTERNAL_URL — cookie name mismatch

Browser creates cookies keyed by the external hostname (sb-myeasycms-*),
but server was using SUPABASE_INTERNAL_URL (sb-supabase-kong-*) — different
keys = server can't find the session = infinite 'please wait' after login.

Both client and server now use the same NEXT_PUBLIC_SUPABASE_URL (external
domain). The SSR reaches Supabase via Traefik → Kong which works fine.

docker-compose.yml

@@ -321,12 +321,10 @@ services:
     environment:
       NODE_ENV: production
       NEXT_PUBLIC_SITE_URL: ${SITE_URL:-http://localhost:3000}
-      # Browser-side: external domain (baked at build time, re-stated here for SSR)
+      # Same URL for browser AND server — keeps Supabase cookie names consistent
       NEXT_PUBLIC_SUPABASE_URL: ${API_EXTERNAL_URL:-http://localhost:8000}
       NEXT_PUBLIC_SUPABASE_PUBLIC_KEY: ${SUPABASE_ANON_KEY}
       NEXT_PUBLIC_DEFAULT_LOCALE: de
-      # Server-side: Docker-internal URL (avoids hairpin NAT / DNS issues)
-      SUPABASE_INTERNAL_URL: http://supabase-kong:8000
       SUPABASE_SECRET_KEY: ${SUPABASE_SERVICE_ROLE_KEY}
       SUPABASE_DB_WEBHOOK_SECRET: ${DB_WEBHOOK_SECRET:-webhooksecret}
       EMAIL_SENDER: ${EMAIL_SENDER:-noreply@myeasycms.de}