fix part 3

backend/app/boards/sharing.py

@@ -2,7 +2,7 @@
 
 import secrets
 import string
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 
 from sqlalchemy.orm import Session
 
@@ -53,12 +53,12 @@ def validate_share_link_token(token: str, db: Session) -> ShareLink | None:
         return None
 
     # Check expiration
-    if share_link.expires_at and share_link.expires_at < datetime.now(timezone.utc):
+    if share_link.expires_at and share_link.expires_at < datetime.now(UTC):
         return None
 
     # Update access tracking
     share_link.access_count += 1
-    share_link.last_accessed_at = datetime.now(timezone.utc)
+    share_link.last_accessed_at = datetime.now(UTC)
     db.commit()
 
     return share_link