fix part 3

backend/app/database/models/group.py

@@ -1,10 +1,10 @@
 """Group database model."""
 
-from datetime import datetime, timezone
+from datetime import datetime
 from typing import TYPE_CHECKING
 from uuid import UUID, uuid4
 
-from sqlalchemy import DateTime, ForeignKey, String, Text
+from sqlalchemy import DateTime, ForeignKey, String, Text, func
 from sqlalchemy.dialects.postgresql import UUID as PGUUID
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
@@ -33,9 +33,9 @@ class Group(Base):
     color: Mapped[str] = mapped_column(String(7), nullable=False)  # Hex color #RRGGBB
     annotation: Mapped[str | None] = mapped_column(Text, nullable=True)
 
-    created_at: Mapped[datetime] = mapped_column(DateTime, nullable=False, default=lambda: datetime.now(timezone.utc))
+    created_at: Mapped[datetime] = mapped_column(DateTime, nullable=False, server_default=func.now())
     updated_at: Mapped[datetime] = mapped_column(
-        DateTime, nullable=False, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc)
+        DateTime, nullable=False, server_default=func.now(), onupdate=func.now()
     )
 
     # Relationships