feat: 初始化微信小程序后端骨架

- NestJS + TypeScript + Prisma + PostgreSQL 工程骨架
- 微信登录安全流程：服务端 code2Session 换 openid 后签发 JWT，
  session_key 缓存于 Redis，不信任前端 openid
- 统一响应/异常处理、JWT 全局鉴权（@Public 豁免）、Swagger 文档
- Prisma 全量核心 schema（用户/分类/商品/设计清单/地址/订单/支付/上传/定制任务）+ seed
- 业务模块空壳（商品/分类/设计清单/地址/订单/支付/上传/BullMQ 队列）
- Docker 多阶段镜像 + 本地/生产 docker-compose
- docs：密钥获取指南、COS SDK 移除记录

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,56 @@
+# 本地开发：仅起 postgres + redis，应用用 npm run start:dev 直连
+# 起容器：docker compose up -d postgres redis
+services:
+  postgres:
+    image: postgres:16-alpine
+    container_name: wxmp-postgres
+    restart: unless-stopped
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: wxmp
+    ports:
+      - "5432:5432"
+    volumes:
+      - wxmp_pg_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres -d wxmp"]
+      interval: 5s
+      timeout: 3s
+      retries: 10
+
+  redis:
+    image: redis:7-alpine
+    container_name: wxmp-redis
+    restart: unless-stopped
+    ports:
+      - "6379:6379"
+    volumes:
+      - wxmp_redis_data:/data
+    healthcheck:
+      test: ["CMD", "redis-cli", "ping"]
+      interval: 5s
+      timeout: 3s
+      retries: 10
+
+  # 本地开发默认不启动 app；需要时用 profile：
+  #   docker compose --profile app up -d
+  app:
+    profiles: ["app"]
+    build:
+      context: .
+      dockerfile: docker/Dockerfile
+    container_name: wxmp-app
+    restart: unless-stopped
+    env_file: .env
+    ports:
+      - "3000:3000"
+    depends_on:
+      postgres:
+        condition: service_healthy
+      redis:
+        condition: service_healthy
+
+volumes:
+  wxmp_pg_data:
+  wxmp_redis_data: