feat: backend env config upgrade - multi-env (dev/prod), DB_* support, Docker compatible

Co-authored-by: Cursor <cursoragent@cursor.com>

deploy/.env.prod.example

@@ -4,8 +4,8 @@
 # 镜像标签
 TAG=latest
 
-# 数据库配置
-DATABASE_URL=postgresql://postgres:CHANGE_ME@db:5432/wecom_ai
+# 数据库配置（backend 也支持仅设置 DB_HOST/DB_PORT/DB_USER/DB_PASSWORD/DB_NAME，自动拼接）
+DATABASE_URL=postgresql+asyncpg://postgres:CHANGE_ME@db:5432/wecom_ai
 DATABASE_URL_SYNC=postgresql://postgres:CHANGE_ME@db:5432/wecom_ai
 POSTGRES_USER=postgres
 POSTGRES_PASSWORD=CHANGE_ME

deploy/docker-compose.prod.yml

@@ -61,8 +61,13 @@ services:
     ports:
       - "80:80"
       - "443:443"
-    volumes:
-      - ./nginx.conf:/etc/nginx/conf.d/default.conf:ro
+    # 注意：镜像构建时已经包含了配置，无需挂载
+    # 如果需要覆盖配置，取消下面的注释并确保 nginx.conf 路径正确
+    # volumes:
+    #   - ./nginx.conf:/etc/nginx/conf.d/default.conf:ro
+    environment:
+      - NGINX_HOST=_
+      - NGINX_PORT=80
     depends_on:
       - backend
       - admin