chore: ruff 代码检查与修复

130 issues auto-fixed (import ordering, UP045/UP006 type annotations),
33 issues manually fixed (E712/E501/E402/E722 + N818 rename + per-file
wechat ignore for N8xx naming conventions). All 33 tests pass.

app/services/notification_service.py

@@ -1,5 +1,5 @@
-from datetime import datetime
-from typing import Any, Dict, List
+from typing import Any
+
 from app.config import settings
 from app.wechat.client import WeChatClient
 
@@ -8,7 +8,7 @@ class NotificationService:
     def __init__(self):
         self.client = WeChatClient()
 
-    async def send(self, announcements: List[Dict[str, Any]]) -> int:
+    async def send(self, announcements: list[dict[str, Any]]) -> int:
         if not settings.wechat_enabled:
             return 0
         if not announcements: