Update transfer-questions CLI to accept user ID instead of username

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app.py

@@ -89,34 +89,36 @@ def create_app(config_name=None):
         return {'status': 'ok', 'message': 'Trivia Game API is running'}, 200
 
     @app.cli.command('transfer-questions')
-    @click.argument('username')
+    @click.argument('user_id', type=int)
-    def transfer_questions(username):
+    def transfer_questions(user_id):
         """Transfer ownership of ALL questions to the specified user.
 
-        USERNAME is the preferred_username of the target user.
+        USER_ID is the database ID of the target user.
         """
         from backend.models import User, Question
 
-        user = User.query.filter_by(preferred_username=username).first()
+        user = User.query.get(user_id)
         if not user:
-            click.echo(f"Error: No user found with username '{username}'")
+            click.echo(f"Error: No user found with id {user_id}")
             click.echo("Available users:")
             for u in User.query.all():
-                click.echo(f"  - {u.preferred_username} (id={u.id}, name={u.name})")
+                click.echo(f"  - id={u.id}, name={u.name or u.preferred_username}")
             raise SystemExit(1)
 
+        display_name = user.name or user.preferred_username
+
         count = Question.query.count()
         if count == 0:
             click.echo("No questions found in the database.")
             return
 
-        click.echo(f"This will transfer ownership of {count} question(s) to '{username}' (id={user.id}).")
+        click.echo(f"This will transfer ownership of {count} question(s) to '{display_name}' (id={user.id}).")
         if not click.confirm("Proceed?"):
             click.echo("Aborted.")
             return
 
         Question.query.update({Question.created_by: user.id})
         db.session.commit()
-        click.echo(f"Successfully transferred {count} question(s) to '{username}'.")
+        click.echo(f"Successfully transferred {count} question(s) to '{display_name}'.")
 
     return app