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/api.ts

@@ -5,6 +5,7 @@ import type {
   DeptGroup,
   RegionGroup,
   CustomerStats,
+  RegionalInventoryStats,
 } from './types';
 
 const BASE = '/api/vehicles';
@@ -69,6 +70,10 @@ export async function fetchCustomerStats(): Promise<CustomerStats[]> {
   return fetchJson<CustomerStats[]>(`${BASE}/customer-stats`);
 }
 
+export async function fetchInventoryStats(): Promise<RegionalInventoryStats[]> {
+  return fetchJson<RegionalInventoryStats[]>(`${BASE}/inventory-stats`);
+}
+
 export async function fetchWeeklyDetail(type: string): Promise<WeeklyDetailItem[]> {
   return fetchJson<WeeklyDetailItem[]>(`${BASE}/weekly-detail?type=${type}`);
 }