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/routes/dashboard.ts

@@ -0,0 +1,100 @@
+import type { DashboardResponse, RuntimeMode } from "../../shared/api";
+import type { ProbeStore } from "../checker/store";
+
+import { formatDuration, jsonResponse, mapCheckResult } from "../helpers";
+import { analyzeIncidentSequence, calculateCurrentStreak, type MetricCheckpoint } from "../metrics";
+import { validateDashboardWindow, validateRecentLimit } from "../middleware";
+
+export function handleDashboard(url: URL, store: ProbeStore, mode: RuntimeMode): Response {
+  const windowResult = validateDashboardWindow(url.searchParams.get("window"), mode);
+  if (windowResult instanceof Response) return windowResult;
+
+  const limitResult = validateRecentLimit(url.searchParams.get("recentLimit"), mode);
+  if (limitResult instanceof Response) return limitResult;
+
+  const targets = store.getTargets();
+  const latestChecksMap = store.getLatestChecksMap();
+  const windowStats = store.getAllTargetWindowStats(windowResult.from, windowResult.to);
+  const recentSamplesMap = store.getAllRecentSamples(limitResult.recentLimit);
+  const incidentStates = groupDashboardIncidentStates(
+    store.getDashboardIncidentStates(windowResult.from, windowResult.to),
+  );
+
+  let up = 0;
+  let down = 0;
+  let lastCheckTime: null | string = null;
+  let incidents = 0;
+
+  const responseTargets: DashboardResponse["targets"] = targets.map((target) => {
+    const latest = latestChecksMap.get(target.id) ?? null;
+    const stats = windowStats.get(target.id) ?? { availability: 0, downChecks: 0, totalChecks: 0, upChecks: 0 };
+    const recentSamples = recentSamplesMap.get(target.id) ?? [];
+    const currentStreak = calculateCurrentStreak(
+      recentSamples.map((sample) => ({
+        durationMs: sample.duration_ms,
+        matched: sample.matched === 1,
+        timestamp: sample.timestamp,
+      })),
+      limitResult.recentLimit,
+    );
+
+    if (latest?.matched === 1) {
+      up++;
+    } else {
+      down++;
+    }
+
+    if (latest && (!lastCheckTime || latest.timestamp > lastCheckTime)) {
+      lastCheckTime = latest.timestamp;
+    }
+
+    incidents += analyzeIncidentSequence(
+      incidentStates.get(target.id) ?? [],
+      windowResult.from,
+      windowResult.to,
+    ).incidentCount;
+
+    return {
+      currentStreak,
+      group: target.grp,
+      id: target.id,
+      interval: formatDuration(target.interval_ms),
+      latestCheck: latest ? mapCheckResult(latest) : null,
+      name: target.name,
+      recentSamples: recentSamples.map((sample) => ({
+        durationMs: sample.duration_ms,
+        timestamp: sample.timestamp,
+        up: sample.matched === 1,
+      })),
+      stats,
+      target: target.target,
+      type: target.type,
+    };
+  });
+
+  const response: DashboardResponse = {
+    summary: {
+      down,
+      incidents,
+      lastCheckTime,
+      total: targets.length,
+      up,
+      window: windowResult,
+    },
+    targets: responseTargets,
+  };
+
+  return jsonResponse(response, { mode });
+}
+
+function groupDashboardIncidentStates(
+  states: Array<{ matched: number; target_id: number; timestamp: string }>,
+): Map<number, MetricCheckpoint[]> {
+  const result = new Map<number, MetricCheckpoint[]>();
+  for (const state of states) {
+    const list = result.get(state.target_id) ?? [];
+    list.push({ durationMs: null, matched: state.matched === 1, timestamp: state.timestamp });
+    result.set(state.target_id, list);
+  }
+  return result;
+}