fix(web): harden route transitions and monitor memory

vehicle-data-platform/apps/web/src/pages/Mileage.tsx

@@ -192,7 +192,7 @@ export function Mileage({
 
   const summaryItems = [
     { label: '区间总里程', value: `${formatKm(statistics?.periodMileageKm)} km`, note: '按车辆和自然日归并' },
-    { label: '统计车辆', value: statistics ? `${statistics.vehicleCount.toLocaleString()} 辆` : '—', note: `${statistics?.recordCount ?? 0} 个有效车辆日` },
+    { label: '统计车辆', value: statistics ? `${(statistics.vehicleCount ?? 0).toLocaleString()} 辆` : '—', note: `${statistics?.recordCount ?? 0} 个有效车辆日` },
     { label: '单车平均', value: `${formatKm(statistics?.averageMileagePerVin)} km`, note: '区间总里程 / 车辆数' },
     { label: '车日均里程', value: `${formatKm(statistics?.averageDailyMileageKm)} km`, note: '有效车辆日平均' }
   ];
@@ -262,7 +262,7 @@ export function Mileage({
         title={(
           <div className="vp-mileage-report-card-title">
             <div><strong>每日里程趋势</strong><span>{filters.dateFrom} 至 {filters.dateTo}</span></div>
-            <Tag color="blue">{statistics?.trend.length ?? 0} 个有效自然日</Tag>
+            <Tag color="blue">{statistics?.trend?.length ?? 0} 个有效自然日</Tag>
           </div>
         )}
       >