feat: 重构为多类型 checker 通用框架，支持 HTTP 与命令检查

- 引入 typed target 判别联合，支持 http 与 command 两种 checker
- expect 重构为有序规则数组，按配置顺序快速失败并生成结构化 failure
- 新增 command runner，支持 exec + args 本地命令执行
- 引入全局并发限制 maxConcurrentChecks 和 size 解析 (KB/MB/GB)
- HTTP/command 各自独立 expect pipeline，应用领域默认成功语义
- SQLite schema、API、Dashboard 全链路调整为 checker 通用契约
- 补充完整测试覆盖（192 tests），更新 README 与示例配置

src/shared/api.ts

@@ -15,15 +15,15 @@ export interface SummaryResponse {
   total: number;
   up: number;
   down: number;
-  avgLatencyMs: number | null;
+  avgDurationMs: number | null;
   lastCheckTime: string | null;
 }
 
 export interface TargetStatus {
   id: number;
   name: string;
-  url: string;
-  method: string;
+  type: string;
+  target: string;
   interval: string;
   latestCheck: CheckResult | null;
   stats: TargetStats;
@@ -33,22 +33,31 @@ export interface TargetStatus {
 export interface TargetStats {
   totalChecks: number;
   availability: number;
-  avgLatencyMs: number | null;
-  p99LatencyMs: number | null;
+  avgDurationMs: number | null;
+  p99DurationMs: number | null;
 }
 
 export interface CheckResult {
   timestamp: string;
   success: boolean;
-  statusCode: number | null;
-  latencyMs: number | null;
-  error: string | null;
   matched: boolean;
+  durationMs: number | null;
+  statusDetail: string | null;
+  failure: CheckFailure | null;
+}
+
+export interface CheckFailure {
+  kind: "error" | "mismatch";
+  phase: string;
+  path: string;
+  expected?: unknown;
+  actual?: unknown;
+  message: string;
 }
 
 export interface TrendPoint {
   hour: string;
-  avgLatencyMs: number | null;
+  avgDurationMs: number | null;
   availability: number;
   totalChecks: number;
 }