Include updatedAt in store-item listings

Backend now returns updated timestamps for variants so the UI can sort by availability.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/store/store-items.service.ts

@@ -971,6 +971,7 @@ export class StoreItemsService {
       isFestival: variant.isFestival,
       sortOrder: variant.sortOrder,
       createdAt: variant.createdAt,
+      updatedAt: variant.updatedAt,
     };
   }