Fix reorder API to properly accept list body parameter

- Add Body() to car_ids parameter in reorder_banners endpoint
- Fixes 422 Unprocessable Entity error when reordering banners

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/api/hero_banners.py

@@ -1,4 +1,4 @@
-from fastapi import APIRouter, Depends, HTTPException, UploadFile, File, Query
+from fastapi import APIRouter, Depends, HTTPException, UploadFile, File, Query, Body
 from sqlalchemy.orm import Session
 from typing import List, Optional
 import os
@@ -325,7 +325,7 @@ def toggle_banner(
 
 @router.put("/admin/reorder")
 def reorder_banners(
-    car_ids: List[int],
+    car_ids: List[int] = Body(...),
     db: Session = Depends(get_db),
     current_user: User = Depends(get_admin_user)
 ):