chore: 整合 migration 文件并优化配置

- 整合 18 个分散的 migration 文件为 5 个模块化文件
- settings.py 支持 .env.local 覆盖 .env
- 移除 user schema 中未使用的 country 字段正则
- 更新 profile protocol 文档移除 country 字段
- pyproject.toml 添加 ruff 到 dev 依赖
- 简化 integration test conftest 邮箱 fixture

docs/protocols/profile/profile-protocol.md

@@ -47,8 +47,7 @@ Response:
     "version": 1,
     "preferences": {
       "language": "zh-CN",
-      "timezone": "Asia/Shanghai",
-      "country": "CN"
+      "timezone": "Asia/Shanghai"
     },
     "privacy": {
       "can_sell": false,
@@ -111,8 +110,7 @@ Request:
     "version": 1,
     "preferences": {
       "language": "zh-CN",
-      "timezone": "Asia/Shanghai",
-      "country": "CN"
+      "timezone": "Asia/Shanghai"
     },
     "privacy": {
       "can_sell": false,