refactor: 引入 Checker 统一接口与 Runner 抽象机制

定义 Checker 接口（resolve/execute/serialize）和 CheckerRegistry
注册中心，消除 engine/config-loader/store 中硬编码类型分支。
按 checker 类型分子包（runner/http/、runner/command/），提取
共享 expect 到 runner/shared/。超时控制通过引擎注入 AbortSignal。
CheckFailure.phase 从联合类型改为 string。配置校验下沉到各
Checker.resolve() 内部。

新增 checker-runner-abstraction spec，更新 DEVELOPMENT.md。

tests/server/checker/runner/shared/duration.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, test } from "bun:test";
+import { checkDuration } from "../../../../../src/server/checker/runner/shared/duration";
+
+describe("checkDuration", () => {
+  test("未配置 maxDurationMs 返回匹配成功", () => {
+    const r = checkDuration(100);
+    expect(r.matched).toBe(true);
+    expect(r.failure).toBeNull();
+  });
+
+  test("duration 在限制内匹配成功", () => {
+    const r = checkDuration(50, 100);
+    expect(r.matched).toBe(true);
+    expect(r.failure).toBeNull();
+  });
+
+  test("duration 等于限制匹配成功", () => {
+    const r = checkDuration(100, 100);
+    expect(r.matched).toBe(true);
+  });
+
+  test("duration 超过限制匹配失败", () => {
+    const r = checkDuration(200, 100);
+    expect(r.matched).toBe(false);
+    expect(r.failure).not.toBeNull();
+    expect(r.failure!.phase).toBe("duration");
+    expect(r.failure!.kind).toBe("mismatch");
+  });
+});