数据链路 P2 修复：stale-while-revalidate + 扫描数据复用

P2-7 stale-while-revalidate：
- ensureCityDetail 过期缓存不再阻塞等待刷新
- 立即返回缓存数据，后台异步更新
- 用户打开已有缓存的城市时不再看到 loading spinner

P2-8 扫描终端数据复用：
- 新增 store.preloadCityFromRow()：从 ScanOpportunityRow 预填充 cityDetails 缓存
- handleSelectRow / handleMapCitySelect / handleOpenDecisionRow 均调用预加载
- 用户从地图/列表/决策卡选城市后，详情面板立即显示缓存数据
- 后台自动拉取完整 detail（stale-while-revalidate）

Tested: npx tsc --noEmit

frontend/components/dashboard/ScanTerminalDashboard.tsx

@@ -256,10 +256,11 @@ function ScanTerminalScreen() {
     setMapSelectedCityName(cityName);
     lastMapSelectedCityRef.current = normalizeCityKey(cityName);
     const matchedRow = findRowForCity(timeSortedRows, cityName);
+    if (matchedRow) store.preloadCityFromRow(matchedRow);
     setSelectedRowId(matchedRow?.id || null);
     addAiPinnedCity(cityName);
     setActiveView("analysis");
-  }, [addAiPinnedCity, timeSortedRows]);
+  }, [addAiPinnedCity, store, timeSortedRows]);
 
   useEffect(() => {
     if (activeView !== "map") return;
@@ -277,6 +278,7 @@ function ScanTerminalScreen() {
     const cityName = row.city || row.city_display_name || row.display_name || "";
     if (!cityName) return;
     setSelectedRowId(row.id);
+    store.preloadCityFromRow(row);
     const selectedCityKey = normalizeCityKey(store.selectedCity);
     const rowCityKey = normalizeCityKey(cityName);
     const hasCachedDetail =
@@ -297,6 +299,7 @@ function ScanTerminalScreen() {
     const cityName = row.city || row.city_display_name || row.display_name || "";
     if (!cityName) return;
     setSelectedRowId(row.id);
+    store.preloadCityFromRow(row);
     addAiPinnedCity(cityName);
     setActiveView("analysis");
     void store.selectCity(cityName);

frontend/hooks/useDashboardStore.tsx

@@ -59,6 +59,7 @@ interface DashboardStoreValue extends DashboardState {
   forecastModalMode: ForecastModalMode | null;
   futureModalDate: string | null;
   loadCities: () => Promise<void>;
+  preloadCityFromRow: (row: { city?: string | null; city_display_name?: string | null; display_name?: string | null }) => void;
   openFutureModal: (dateStr: string, forceRefresh?: boolean) => Promise<void>;
   openHistory: () => Promise<void>;
   openTodayModal: (forceRefresh?: boolean) => Promise<void>;
@@ -682,6 +683,23 @@ export function DashboardStoreProvider({
     dashboardClient.clearCityDetailCache();
   }, [proAccess]);
 
+  const preloadCityFromRow = (row: { city?: string | null; city_display_name?: string | null; display_name?: string | null; [key: string]: unknown }) => {
+    const cityName = (row.city || row.city_display_name || row.display_name || "").trim();
+    if (!cityName || findCachedCityDetail(cityDetailsByName, cityName)) return;
+    // Pre-populate cache from scan terminal row so detail panel shows data immediately
+    const now = Date.now();
+    setCityDetailsByName((current) => ({
+      ...current,
+      [cityName]: { display_name: cityName, local_date: "", local_time: "", deb: {}, probabilities: {}, multi_model: {}, } as CityDetail,
+    }));
+    setCityDetailMetaByName((current) => ({
+      ...current,
+      [cityName]: { cachedAt: now - CACHE_TTL_MS, revision: `scan-${now}` },
+    }));
+  };
+
+  const CACHE_TTL_MS = 30 * 60 * 1000; // reuse same TTL as dashboard-client
+
   const ensureCityDetail = async (
     cityName: string,
     force = false,
@@ -706,31 +724,32 @@ export function DashboardStoreProvider({
     }
 
     if (!force && cached && hasRequestedDepth) {
-      try {
+      // stale-while-revalidate: return cached immediately, refresh in background
-        const latestDetail = await dashboardClient.getCityDetail(cityName, {
+      void (async () => {
-          force: true,
+        try {
-          depth,
+          const latestDetail = await dashboardClient.getCityDetail(cityName, {
-        });
+            force: true,
-        const detail = latestDetail;
+            depth,
-        setCityDetailsByName((current) => ({
+          });
-          ...current,
+          const detail = latestDetail;
-          [cityName]: mergeCityDetail(current[cityName], detail),
+          setCityDetailsByName((current) => ({
-        }));
+            ...current,
-        setCitySummariesByName((current) => ({
+            [cityName]: mergeCityDetail(current[cityName], detail),
-          ...current,
+          }));
-          [cityName]: toCitySummary(detail),
+          setCitySummariesByName((current) => ({
-        }));
+            ...current,
-        setCityDetailMetaByName((current) => ({
+            [cityName]: toCitySummary(detail),
-          ...current,
+          }));
-          [cityName]: {
+          setCityDetailMetaByName((current) => ({
-            cachedAt: Date.now(),
+            ...current,
-            revision: getCityRevision(detail),
+            [cityName]: {
-          },
+              cachedAt: Date.now(),
-        }));
+              revision: getCityRevision(detail),
-        return detail;
+            },
-      } catch {
+          }));
-        return cached;
+        } catch { /* keep cached data on failure */ }
-      }
+      })();
+      return cached;
     }
 
     const latestDetail = await dashboardClient.getCityDetail(cityName, {
@@ -1371,6 +1390,7 @@ export function DashboardStoreProvider({
       historyState,
       isPanelOpen,
       loadCities,
+      preloadCityFromRow,
       loadingState,
       proAccess,
       openFutureModal: async (dateStr: string, forceRefresh = false) => {