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/web/components/TargetRow.tsx

@@ -11,7 +11,7 @@ interface TargetRowProps {
 export function TargetRow({ target, expanded, onToggle }: TargetRowProps) {
   const isUp = target.latestCheck?.success && target.latestCheck?.matched;
 
-  const sparklineData = target.sparkline.map((latency) => ({ latency }));
+  const sparklineData = target.sparkline.map((duration) => ({ duration }));
 
   return (
     <tr className={`target-row ${expanded ? "expanded" : ""}`} onClick={onToggle}>
@@ -19,11 +19,11 @@ export function TargetRow({ target, expanded, onToggle }: TargetRowProps) {
         <StatusDot up={!!isUp} />
       </td>
       <td className="col-name">{target.name}</td>
-      <td className="col-url">{target.url}</td>
-      <td className="col-method">{target.method}</td>
-      <td className="col-latency">
-        {target.latestCheck?.latencyMs !== null && target.latestCheck?.latencyMs !== undefined
-          ? `${Math.round(target.latestCheck.latencyMs)}ms`
+      <td className="col-target">{target.target}</td>
+      <td className="col-type">{target.type === "http" ? "HTTP" : "Command"}</td>
+      <td className="col-duration">
+        {target.latestCheck?.durationMs !== null && target.latestCheck?.durationMs !== undefined
+          ? `${Math.round(target.latestCheck.durationMs)}ms`
           : "-"}
       </td>
       <td className="col-sparkline">