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/server/server.ts

@@ -4,12 +4,11 @@ import type { RuntimeConfig } from "./config";
 
 import homepage from "../web/index.html";
 import { createApiError, jsonResponse } from "./helpers";
+import { handleDashboard } from "./routes/dashboard";
 import { handleHealth } from "./routes/health";
 import { handleHistory } from "./routes/history";
 import { handleMeta } from "./routes/meta";
-import { handleSummary } from "./routes/summary";
-import { handleTargets } from "./routes/targets";
-import { handleTrend } from "./routes/trend";
+import { handleMetrics } from "./routes/metrics";
 
 export interface StartServerOptions {
   config: RuntimeConfig;
@@ -30,20 +29,17 @@ export function startServer(options: StartServerOptions) {
     routes: {
       "/*": homepage,
       "/api/*": () => jsonResponse(createApiError("API route not found", 404), { mode, status: 404 }),
+      "/api/dashboard": {
+        GET: (req) => handleDashboard(new URL(req.url), store, mode),
+      },
       "/api/meta": {
         GET: () => handleMeta(mode),
       },
-      "/api/summary": {
-        GET: () => handleSummary(store, mode),
-      },
-      "/api/targets": {
-        GET: () => handleTargets(store, mode),
-      },
       "/api/targets/:id/history": {
         GET: (req) => handleHistory(req.params.id, new URL(req.url), store, mode),
       },
-      "/api/targets/:id/trend": {
-        GET: (req) => handleTrend(req.params.id, new URL(req.url), store, mode),
+      "/api/targets/:id/metrics": {
+        GET: (req) => handleMetrics(req.params.id, new URL(req.url), store, mode),
       },
       "/health": {
         GET: () => handleHealth(mode),