Fix banner reorder API with proper request schema

- Create BannerReorderRequest Pydantic model for reorder endpoint
- Update frontend to send car_ids wrapped in object
- Fixes 422 Unprocessable Entity on reorder API

🤖 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

@@ -12,6 +12,7 @@ from ..schemas.hero_banner import (
     HeroBannerCreate, HeroBannerUpdate, HeroBannerResponse,
     HeroBannerListResponse, HeroBannerLocalizedResponse,
     HeroBannerSettingsUpdate, HeroBannerSettingsResponse,
+    BannerReorderRequest,
 )
 from .auth import get_current_user
 from ..models import User
@@ -325,7 +326,7 @@ def toggle_banner(
 
 @router.put("/admin/reorder")
 def reorder_banners(
-    car_ids: List[int] = Body(...),
+    request: BannerReorderRequest,
     db: Session = Depends(get_db),
     current_user: User = Depends(get_admin_user)
 ):
@@ -333,13 +334,13 @@ def reorder_banners(
 
     car_ids: 배너 차량 ID 목록 (원하는 순서대로)
     """
-    for order, car_id in enumerate(car_ids):
+    for order, car_id in enumerate(request.car_ids):
         banner = db.query(HeroBanner).filter(HeroBanner.car_id == car_id).first()
         if banner:
             banner.display_order = order
 
     db.commit()
-    return {"message": "Banner order updated", "count": len(car_ids)}
+    return {"message": "Banner order updated", "count": len(request.car_ids)}
 
 
 @router.get("/admin/banner-cars")