Fix 422 error on /admin/banner-cars endpoint

Move /admin/banner-cars route before /admin/{banner_id} to fix route
matching order. FastAPI was matching "banner-cars" as a path parameter
and failing to convert it to an integer.

🤖 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

@@ -124,6 +124,25 @@ def admin_get_banners(
     return banners
 
 
+@router.get("/admin/banner-cars")
+def get_banner_cars(
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_admin_user)
+):
+    """배너 등록된 차량 목록 조회 (Admin)
+
+    display_order 순으로 정렬된 차량 ID 목록 반환
+    """
+    banners = db.query(HeroBanner).filter(
+        HeroBanner.car_id.isnot(None)
+    ).order_by(HeroBanner.display_order.asc()).all()
+
+    return {
+        "car_ids": [b.car_id for b in banners],
+        "count": len(banners)
+    }
+
+
 @router.get("/admin/{banner_id}", response_model=HeroBannerResponse)
 def admin_get_banner(
     banner_id: int,
@@ -341,22 +360,3 @@ def reorder_banners(
 
     db.commit()
     return {"message": "Banner order updated", "count": len(request.car_ids)}
-
-
-@router.get("/admin/banner-cars")
-def get_banner_cars(
-    db: Session = Depends(get_db),
-    current_user: User = Depends(get_admin_user)
-):
-    """배너 등록된 차량 목록 조회 (Admin)
-
-    display_order 순으로 정렬된 차량 ID 목록 반환
-    """
-    banners = db.query(HeroBanner).filter(
-        HeroBanner.car_id.isnot(None)
-    ).order_by(HeroBanner.display_order.asc()).all()
-
-    return {
-        "car_ids": [b.car_id for b in banners],
-        "count": len(banners)
-    }