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/api/router.py

@@ -1,5 +1,7 @@
 from fastapi import APIRouter
-from app.api import announcements, crawl, wechat, scheduler as scheduler_module
+
+from app.api import announcements, crawl, wechat
+from app.api import scheduler as scheduler_module
 
 api_router = APIRouter(prefix="/api/v1")
 api_router.include_router(announcements.router, tags=["announcements"])