feat: 将 demo 项目转化为 HTTP 拨测监控工具

新增 YAML 配置解析（Bun 内置 YAML）、SQLite 数据存储（bun:sqlite）、按 interval 分组并发拨测引擎、REST API（/api/summary、/api/targets、/api/targets/:id/history、/api/targets/:id/trend）、React 前端 Dashboard（统计卡片、目标表格、可展开详情面板、recharts 趋势图）。CLI 简化为仅接受配置文件路径。移除 /api/demo 路由和相关 demo 代码。保留 /health、静态资源服务和 SPA fallback。

src/shared/api.ts

@@ -1,16 +1,5 @@
 export type RuntimeMode = "development" | "production" | "test";
 
-export interface DemoResponse {
-  message: string;
-  runtime: {
-    mode: RuntimeMode;
-    bunVersion: string;
-    platform: string;
-    arch: string;
-    timestamp: string;
-  };
-}
-
 export interface HealthResponse {
   ok: true;
   service: "gateway-checker";
@@ -21,3 +10,45 @@ export interface ApiErrorResponse {
   error: string;
   status: number;
 }
+
+export interface SummaryResponse {
+  total: number;
+  up: number;
+  down: number;
+  avgLatencyMs: number | null;
+  lastCheckTime: string | null;
+}
+
+export interface TargetStatus {
+  id: number;
+  name: string;
+  url: string;
+  method: string;
+  interval: string;
+  latestCheck: CheckResult | null;
+  stats: TargetStats;
+  sparkline: number[];
+}
+
+export interface TargetStats {
+  totalChecks: number;
+  availability: number;
+  avgLatencyMs: number | null;
+  p99LatencyMs: number | null;
+}
+
+export interface CheckResult {
+  timestamp: string;
+  success: boolean;
+  statusCode: number | null;
+  latencyMs: number | null;
+  error: string | null;
+  matched: boolean;
+}
+
+export interface TrendPoint {
+  hour: string;
+  avgLatencyMs: number | null;
+  availability: number;
+  totalChecks: number;
+}