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/models/schemas.py

@@ -1,5 +1,5 @@
 from datetime import datetime
-from typing import Optional
+
 from pydantic import BaseModel
 
 
@@ -29,14 +29,14 @@ class AnnouncementListResponse(BaseModel):
 
 
 class CrawlTriggerRequest(BaseModel):
-    keywords: Optional[list[str]] = None
-    sources: Optional[list[str]] = None
+    keywords: list[str] | None = None
+    sources: list[str] | None = None
     manual: bool = False
 
 
 class CrawlStatusResponse(BaseModel):
     running: bool
-    last_crawl_time: Optional[datetime] = None
+    last_crawl_time: datetime | None = None
     total_sources: int
 
 
@@ -53,4 +53,4 @@ class SourcesResponse(BaseModel):
 class JobResponse(BaseModel):
     id: str
     name: str
-    next_run_time: Optional[str] = None
+    next_run_time: str | None = None