Disable touch drag & drop, warn on car delete with reservations, configure backend URL

Co-authored-by: pdf114514 <57948770+pdf114514@users.noreply.github.com>
Agent-Logs-Url: https://github.com/pdf114514/CarReservation/sessions/cd194ca1-b339-4f2f-b717-31a0ba193964

frontend/src/components/CarManagement.jsx

@@ -4,6 +4,7 @@ import styles from './CarManagement.module.css';
 
 export default function CarManagement() {
   const [cars, setCars] = useState([]);
+  const [reservations, setReservations] = useState([]);
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState(null);
   const [newCarName, setNewCarName] = useState('');
@@ -16,8 +17,9 @@ export default function CarManagement() {
   const loadCars = async () => {
     try {
       setLoading(true);
-      const data = await api.getCars();
-      setCars(data);
+      const [carsData, resData] = await Promise.all([api.getCars(), api.getReservations()]);
+      setCars(carsData);
+      setReservations(resData);
       setError(null);
     } catch (e) {
       setError(e.message);
@@ -47,7 +49,11 @@ export default function CarManagement() {
   };
 
   const handleDelete = async (id, name) => {
-    if (!confirm(`「${name}」を削除しますか？\n関連する予約もすべて削除されます。`)) return;
+    const carReservations = reservations.filter((r) => r.car_id === id);
+    const message = carReservations.length > 0
+      ? `「${name}」を削除しますか？\n⚠ この代車には ${carReservations.length} 件の予約があります。削除するとこれらの予約もすべて削除されます。`
+      : `「${name}」を削除しますか？\n関連する予約もすべて削除されます。`;
+    if (!confirm(message)) return;
     try {
       await api.deleteCar(id);
       await loadCars();