feat: Dashboard 刷新频率可配置 — RadioGroup 选择器、动态轮询间隔、手动刷新按钮

- useDashboard hook 改为接受 refetchInterval 动态参数，移除固定 8 秒常量
- Header operations 区域重构为 RadioGroup（手动/10秒/30秒/1分钟/5分钟）+ 倒计时/刷新按钮
- 新增 formatCountdown 工具函数及单元测试
- 新增 .dashboard-refresh-control 和 .dashboard-countdown CSS 类
- 同步更新 DEVELOPMENT.md、README.md、主 specs

src/web/hooks/use-queries.ts

@@ -9,19 +9,17 @@ const queryKeys = {
     ["metrics", targetId, from, to, bucket] as const,
 };
 
-export const DASHBOARD_REFRESH_INTERVAL_MS = 8000;
-
 export async function fetchJson<T>(url: string): Promise<T> {
   const response = await fetch(url);
   if (!response.ok) throw new Error(`HTTP ${response.status}`);
   return response.json() as Promise<T>;
 }
 
-export function useDashboard() {
+export function useDashboard(refetchInterval: false | number) {
   return useQuery({
     queryFn: () => fetchJson<DashboardResponse>("/api/dashboard?window=24h&recentLimit=30"),
     queryKey: queryKeys.dashboard(),
-    refetchInterval: DASHBOARD_REFRESH_INTERVAL_MS,
+    refetchInterval,
     refetchIntervalInBackground: false,
   });
 }

src/web/hooks/use-target-detail.ts

@@ -17,7 +17,7 @@ export function useTargetDetail() {
   const [timeTo, setTimeTo] = useState("");
   const [historyPage, setHistoryPage] = useState(1);
 
-  const { data: dashboardData } = useDashboard();
+  const { data: dashboardData } = useDashboard(false);
   const selectedTarget =
     selectedTargetId !== null
       ? (dashboardData?.targets.find((target) => target.id === selectedTargetId) ?? null)