fix: path traversal via URL-encoded ../, Feb 29 leap year crash, missing response_model, dead code, duplicate utcnow

api/app/models/user_settings.py

@@ -1,12 +1,6 @@
 from sqlalchemy import Column, Integer, String, Text, DateTime, Date
-from datetime import datetime, timezone, date
 from app.database import Base
-
-
-def utcnow():
-    """统一获取 UTC 时间的工厂函数"""
-    return datetime.now(timezone.utc)
-
+from app.utils.datetime import utcnow
 
 class UserSettings(Base):
     """用户设置模型（单例，始终只有一条记录 id=1）"""