refactor: update timestamp handling to use timezone-aware datetime

app/services/credit_service.py

@@ -2,6 +2,7 @@
 
 import logging
 from datetime import datetime
+from zoneinfo import ZoneInfo
 
 from app.database import db
 from app.models.user import User
@@ -62,7 +63,7 @@ class CreditService:
 
                 if credits_added > 0:
                     user.credits = new_credits
-                    user.updated_at = datetime.utcnow()
+                    user.updated_at = datetime.now(tz=ZoneInfo("UTC"))
                     total_credits_added += credits_added
 
                     logger.debug(