feat: add inventory statistics section, adapt to latest prototype

- Add GET /api/vehicles/inventory-stats endpoint that groups inventory vehicles by macro-region, city, brand, type, model, and batch
- Add RegionalInventoryStats type and fetchInventoryStats API function
- Add full inventory statistics section with region/model tabs, filters, desktop table, and mobile views
- Add modal filters (plate number, model, brand, location search) to vehicle detail modal
- Update modal header to support title field for contextual naming

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/types.ts

@@ -114,6 +114,16 @@ export interface VehicleListItem {
   orgName: string | null;
 }
 
+export interface RegionalInventoryStats {
+  region: string;
+  city: string;
+  brand: string;
+  type: string;
+  model: string;
+  batch: string;
+  quantity: number;
+}
+
 export interface ManagerStats {
   manager: string;
   department: string;