feat: 前端指标体系增强 — Dashboard/Metrics API、2×4 统计区、趋势图面积+异常标记、连续状态列

- 新增 GET /api/dashboard 合并原 summary+targets 首屏接口
- 新增 GET /api/targets/:id/metrics 合并原 stats+trend 概览接口
- 后端指标纯函数：可用率、百分位、故障段分析、连续状态、UTC 小时分桶
- ProbeStore 窗口取数方法替代全量历史查询
- SummaryCards 扩展为 4 卡片（新增异常事件数）+ 数据新鲜度展示
- 表格新增「连续」列（Tag 渲染 capped 状态）
- OverviewTab 重构为 2×4 Statistic 多维度布局
- TrendChart 改为延迟范围面积图 + 红色异常标记点
- 删除旧路由（summary/targets/trend）和 computeTrendStats
- 同步 delta specs 到主 specs 并归档变更

src/web/hooks/use-queries.ts

@@ -1,11 +1,12 @@
 import { useQuery } from "@tanstack/react-query";
 
-import type { MetaResponse, SummaryResponse, TargetStatus } from "../../shared/api";
+import type { DashboardResponse, MetaResponse, TargetMetricsResponse } from "../../shared/api";
 
 const queryKeys = {
+  dashboard: () => ["dashboard", "24h", 30] as const,
   meta: () => ["meta"] as const,
-  summary: () => ["summary"] as const,
-  targets: () => ["targets"] as const,
+  metrics: (targetId: number, from: string, to: string, bucket: "1h") =>
+    ["metrics", targetId, from, to, bucket] as const,
 };
 
 export async function fetchJson<T>(url: string): Promise<T> {
@@ -14,6 +15,15 @@ export async function fetchJson<T>(url: string): Promise<T> {
   return response.json() as Promise<T>;
 }
 
+export function useDashboard() {
+  return useQuery({
+    queryFn: () => fetchJson<DashboardResponse>("/api/dashboard?window=24h&recentLimit=30"),
+    queryKey: queryKeys.dashboard(),
+    refetchInterval: 8000,
+    refetchIntervalInBackground: false,
+  });
+}
+
 export function useMeta() {
   return useQuery({
     queryFn: () => fetchJson<MetaResponse>("/api/meta"),
@@ -22,20 +32,15 @@ export function useMeta() {
   });
 }
 
-export function useSummary() {
+export function useTargetMetrics(targetId: null | number, from: string, to: string, bucket: "1h") {
   return useQuery({
-    queryFn: () => fetchJson<SummaryResponse>("/api/summary"),
-    queryKey: queryKeys.summary(),
-    refetchInterval: 8000,
-    refetchIntervalInBackground: false,
-  });
-}
-
-export function useTargets() {
-  return useQuery({
-    queryFn: () => fetchJson<TargetStatus[]>("/api/targets"),
-    queryKey: queryKeys.targets(),
-    refetchInterval: 8000,
-    refetchIntervalInBackground: false,
+    enabled: targetId !== null && !!from && !!to,
+    queryFn: () => {
+      if (targetId === null) throw new Error("未选择目标");
+      return fetchJson<TargetMetricsResponse>(
+        `/api/targets/${targetId}/metrics?from=${encodeURIComponent(from)}&to=${encodeURIComponent(to)}&bucket=${bucket}`,
+      );
+    },
+    queryKey: targetId !== null && from && to ? queryKeys.metrics(targetId, from, to, bucket) : ["metrics", "disabled"],
   });
 }