图表 stats bar 温度数字 60 秒级轻量轮询

liveTemp state 独立于 hourly 缓存，每 60s fetch /api/city/{city}/summary。
只取 current.temp，不触发 _analyze() 重算。
图表曲线保持 5min TTL，顶部数字最快 1min 级更新。

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

@@ -34,10 +34,13 @@ export function runTests() {
   );
   assert(
     chartSource.includes("DASHBOARD_REFRESH_POLICY_MS.metar") &&
-      !chartSource.includes("setInterval(") &&
       !chartSource.includes("window.setInterval"),
     "selected city detail chart cache should align with 5-minute scan/metar cadence",
   );
+  assert(
+    chartSource.includes("setInterval(fetchLiveTemp, 60_000)"),
+    "selected city chart should poll live temperature every 60 seconds via lightweight summary endpoint",
+  );
   assert(
     chartSource.includes("_hourlyRequestCache") &&
       chartSource.includes("seedHourlyForecastFromRow") &&