修复高风险预警邮件通知并补充测试

tests/unit/api/test_risk_controller.py

@@ -56,6 +56,10 @@ class StubRiskScanService:
     def __init__(self, _session: Any) -> None:
         pass
 
+    @classmethod
+    def from_settings(cls, session: Any) -> "StubRiskScanService":
+        return cls(session)
+
     async def scan(self, _context: RequestContext) -> dict[str, Any]:
         return {"message": "规则扫描完成", "created_count": 2, "high_risk_count": 1}