better time usings

src/server/database/models.py

@@ -11,7 +11,7 @@ Models:
 """
 from __future__ import annotations
 
-from datetime import datetime
+from datetime import datetime, timezone
 from enum import Enum
 from typing import List, Optional
 
@@ -422,7 +422,7 @@ class UserSession(Base, TimestampMixin):
     @property
     def is_expired(self) -> bool:
         """Check if session has expired."""
-        return datetime.utcnow() > self.expires_at
+        return datetime.now(timezone.utc) > self.expires_at
     
     def revoke(self) -> None:
         """Revoke this session."""