修复城市决策卡切换时地图白屏和第二城市加载失败

- MapCanvas 改为始终挂载，视图切换用 display:none 隐藏而非卸载，
  避免 Leaflet 重初始化时容器尺寸为 0 导致白屏
- handleMapCitySelect 在 matchedRow 为空时主动调用 ensureCityDetail
  预加载城市详情，不再依赖 hydration 队列异步补拉

frontend/components/dashboard/scan-terminal/__tests__/temperatureChartData.test.ts

@@ -78,7 +78,7 @@ export function runTests() {
     "Ankara chart should build the DEB original path from MGM hourly data when Open-Meteo hourly is unavailable",
   );
   assert(
-    ankaraChartData?.datasets.debSeries.length >= 4,
+    (ankaraChartData?.datasets.debSeries.length ?? 0) >= 4,
     "Ankara chart should build the DEB original path from MGM hourly data",
   );
   assert(