feat: Go 重写后端，替换 Python FastAPI

用 Go (Gin + GORM + SQLite) 重写整个后端：
- 单二进制部署，不依赖 Python/pip/SDK
- net/http 原生客户端，无 Cloudflare TLS 指纹问题
- 多阶段 Dockerfile：Node 构建前端 + Go 构建后端 + Alpine 运行
- 内存占用从 ~95MB 降至 ~3MB
- 完整保留所有 API 路由、JWT 认证、API Key 权限、审计日志

docker-compose.yml

@@ -1,11 +1,9 @@
-version: "3.8"
-
 services:
-  backend:
+  app:
     build:
       context: .
-      dockerfile: backend/Dockerfile
-    container_name: airwallex-backend
+      dockerfile: Dockerfile
+    container_name: airwallex-admin
     ports:
       - "8000:8000"
     volumes:
@@ -13,18 +11,7 @@ services:
     env_file:
       - backend/.env
     environment:
-      - DATABASE_URL=sqlite:///./data/airwallex.db
-    restart: unless-stopped
-
-  frontend:
-    build:
-      context: frontend
-      dockerfile: Dockerfile
-    container_name: airwallex-frontend
-    ports:
-      - "3000:3000"
-    depends_on:
-      - backend
+      - GIN_MODE=release
     restart: unless-stopped
 
 volumes: