feat: target 时间配置校验，interval 最小 10s，timeout 不大于 interval

在配置加载阶段新增通用 target 时间字段语义校验：
- interval 解析后不得小于 10s
- timeout 解析后不得大于同一 target 的 interval
- 默认值（30s / 10s）参与校验
- 变量引用先解析再校验
- 格式错误优先于关系错误，避免级联提示

tests/server/checker/config-loader.test.ts

@@ -886,6 +886,144 @@ targets:
     await expectConfigLoadError(configPath, "无效的时长格式");
   });
 
+  test("interval 小于 10s 抛出错误", async () => {
+    const configPath = join(tempDir, "interval-too-small.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - name: "t"
+    id: "t"
+    type: http
+    interval: "9s"
+    http:
+      url: "http://a.com"
+`,
+    );
+    await expectConfigLoadError(configPath, "interval 不能小于 10s");
+  });
+
+  test("interval 9999ms 抛出错误", async () => {
+    const configPath = join(tempDir, "interval-9999ms.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - name: "t"
+    id: "t"
+    type: http
+    interval: "9999ms"
+    http:
+      url: "http://a.com"
+`,
+    );
+    await expectConfigLoadError(configPath, "interval 不能小于 10s");
+  });
+
+  test("interval 10s 通过", async () => {
+    const configPath = join(tempDir, "interval-10s.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - name: "t"
+    id: "t"
+    type: http
+    interval: "10s"
+    http:
+      url: "http://a.com"
+`,
+    );
+    const config = await loadConfig(configPath);
+    expect(config.targets[0]!.intervalMs).toBe(10000);
+  });
+
+  test("interval 10000ms 通过", async () => {
+    const configPath = join(tempDir, "interval-10000ms.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - name: "t"
+    id: "t"
+    type: http
+    interval: "10000ms"
+    http:
+      url: "http://a.com"
+`,
+    );
+    const config = await loadConfig(configPath);
+    expect(config.targets[0]!.intervalMs).toBe(10000);
+  });
+
+  test("timeout 大于 interval 抛出错误", async () => {
+    const configPath = join(tempDir, "timeout-gt-interval.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - name: "t"
+    id: "t"
+    type: http
+    interval: "10s"
+    timeout: "30s"
+    http:
+      url: "http://a.com"
+`,
+    );
+    await expectConfigLoadError(configPath, "timeout 不能大于 interval");
+  });
+
+  test("timeout 等于 interval 通过", async () => {
+    const configPath = join(tempDir, "timeout-eq-interval.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - name: "t"
+    id: "t"
+    type: http
+    interval: "30s"
+    timeout: "30s"
+    http:
+      url: "http://a.com"
+`,
+    );
+    const config = await loadConfig(configPath);
+    expect(config.targets[0]!.intervalMs).toBe(30000);
+    expect(config.targets[0]!.timeoutMs).toBe(30000);
+  });
+
+  test("变量解析后 interval 小于 10s 抛出错误", async () => {
+    const configPath = join(tempDir, "var-interval-too-small.yaml");
+    await writeFile(
+      configPath,
+      `variables:
+  check_interval: "5s"
+targets:
+  - name: "t"
+    id: "t"
+    type: http
+    interval: "\${check_interval}"
+    http:
+      url: "http://a.com"
+`,
+    );
+    await expectConfigLoadError(configPath, "interval 不能小于 10s");
+  });
+
+  test("变量解析后 timeout 大于 interval 抛出错误", async () => {
+    const configPath = join(tempDir, "var-timeout-gt-interval.yaml");
+    await writeFile(
+      configPath,
+      `variables:
+  check_timeout: "60s"
+targets:
+  - name: "t"
+    id: "t"
+    type: http
+    timeout: "\${check_timeout}"
+    http:
+      url: "http://a.com"
+`,
+    );
+    await expectConfigLoadError(configPath, "timeout 不能大于 interval");
+  });
+
   test("解析 expect 配置", async () => {
     const configPath = join(tempDir, "expect.yaml");
     await writeFile(