fixed all test issues

src/server/database/models.py

@@ -422,7 +422,11 @@ class UserSession(Base, TimestampMixin):
     @property
     def is_expired(self) -> bool:
         """Check if session has expired."""
-        return datetime.now(timezone.utc) > self.expires_at
+        # Ensure expires_at is timezone-aware for comparison
+        expires_at = self.expires_at
+        if expires_at.tzinfo is None:
+            expires_at = expires_at.replace(tzinfo=timezone.utc)
+        return datetime.now(timezone.utc) > expires_at
     
     def revoke(self) -> None:
         """Revoke this session."""