fix: 修复后端代码违规并更新协议文档

- 修复 notifications 模块 datetime.now() 缺少时区问题
- 用 ApiProblemError 替换 BaseService 中的 HTTPException
- 更新协议文档：添加错误码、繁体字段、邀请相关协议
- 升级 Docker 镜像版本

backend/src/v1/notifications/service.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
-from datetime import datetime
+from datetime import datetime, timezone
 from uuid import UUID
 
 from core.http.errors import ApiProblemError, problem_payload
@@ -113,7 +113,7 @@ class NotificationService:
             body=n.body,
             payload=payload,
             is_read=True,
-            read_at=un.read_at or datetime.now(),
+            read_at=un.read_at or datetime.now(timezone.utc),
             created_at=un.created_at,
         )