fix: 区域统计客户筛选生效，后端region-stats支持过滤参数

- 后端/region-stats新增customer/city/region查询参数
- 前端regionFilters变化时重新请求后端数据
- 移除前端冗余过滤逻辑，由后端统一处理

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

src/server/routes/vehicles.ts

@@ -724,7 +724,11 @@ app.get('/dept-stats', async (c) => {
 // GET /api/vehicles/region-stats — macro-region with city drill-down
 app.get('/region-stats', async (c) => {
   const vehicles = await getVehicles();
-  const operating = vehicles.filter((v) => v.status === 'Operating' || v.status === 'Pending');
+  const { customer, city: filterCity, region: filterRegion } = c.req.query();
+  let operating = vehicles.filter((v) => v.status === 'Operating' || v.status === 'Pending');
+  if (customer) operating = operating.filter((v) => v.customerName === customer);
+  if (filterCity) operating = operating.filter((v) => resolveCity(v.city, v.province) === filterCity);
+  if (filterRegion) operating = operating.filter((v) => mapMacroRegion(v.province, v.city) === filterRegion);
 
   const regionCityMap = new Map<string, Map<string, Vehicle[]>>();
   for (const v of operating) {