fix(docker): remove network_mode for Dokploy compatibility

Dokploy injects 'networks' into all compose services for Traefik routing,
which is mutually exclusive with 'network_mode: service:supabase-kong'.

Changes:
- Remove network_mode from app service
- App server-side Supabase URL: http://supabase-kong:8000 (Docker DNS)
- App browser-side Supabase URL: ${API_EXTERNAL_URL} (external domain)
- Kong catch-all route: app:3000 instead of localhost:3000

docker/kong.yml

@@ -88,7 +88,7 @@ services:
 
   # Next.js App (catch-all — must be last so API routes take priority)
   - name: app
-    url: http://localhost:3000/
+    url: http://app:3000/
     routes:
       - name: app-routes
         strip_path: false