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/crawl.py

@@ -1,4 +1,5 @@
 from fastapi import APIRouter
+
 from app.api.deps import get_crawl_service
 from app.models.schemas import CrawlTriggerRequest
 
@@ -34,6 +35,7 @@ async def crawl_status():
 @router.get("/crawl/sources")
 async def crawl_sources():
     import json
+
     from app.config import settings
     sources = json.loads(settings.announcement_sources)
     return {