fix(api-gateway): 使用官方 Docker Hub 镜像解决拉取问题

- 使用 docker.io/kong/kong-gateway:3.5 官方镜像
- 使用 docker.io/library/postgres:16-alpine 官方镜像
- 保留数据库模式，完整功能支持

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/api-gateway/docker-compose.yml

@@ -13,7 +13,7 @@ services:
   # Kong Database
   # ===========================================================================
   kong-db:
-    image: postgres:16-alpine
+    image: docker.io/library/postgres:16-alpine
     container_name: rwa-kong-db
     environment:
       POSTGRES_USER: kong
@@ -34,7 +34,7 @@ services:
   # Kong Migrations (只运行一次)
   # ===========================================================================
   kong-migrations:
-    image: kong:3.5-alpine
+    image: docker.io/kong/kong-gateway:3.5
     container_name: rwa-kong-migrations
     command: kong migrations bootstrap
     environment:
@@ -54,7 +54,7 @@ services:
   # Kong API Gateway
   # ===========================================================================
   kong:
-    image: kong:3.5-alpine
+    image: docker.io/kong/kong-gateway:3.5
     container_name: rwa-kong
     environment:
       KONG_DATABASE: postgres