feat: 新增本机 CPU checker

- 新增 type: cpu checker，基于 os.cpus() 两次快照计算 CPU 使用率
- 配置项：sampleDuration（默认 1s）、includePerCore（默认 false）
- expect 字段：usagePercent、idlePercent、maxCoreUsagePercent、minCoreUsagePercent、durationMs
- idlePercent 与 usagePercent 互补恒等于 100，百分比范围 0-100
- logicalCoreCount 仅输出到 observation，不作为 expect 字段
- 不暴露 userPercent / systemPercent
- 语义校验禁止 sampleDuration >= timeout
- 支持 AbortSignal 超时取消
- 完整测试覆盖：schema、validate、normalize、resolve、calculate、execute、expect、config-loader
- 新增用户文档 docs/user/checkers/cpu.md
- 更新 checker 索引、配置类型列表、示例配置和 schema

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

@@ -2270,6 +2270,82 @@ targets:
     );
   });
 
+  test("解析最简 cpu 配置", async () => {
+    const configPath = join(tempDir, "minimal-cpu.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - id: "local-cpu"
+    type: cpu
+    cpu: {}
+`,
+    );
+
+    const config = await loadConfig(configPath);
+    expect(config.targets).toHaveLength(1);
+    const t = config.targets[0]! as Record<string, unknown>;
+    expect(t["type"]).toBe("cpu");
+    expect((t["cpu"] as Record<string, unknown>)["sampleDurationMs"]).toBe(1000);
+    expect((t["cpu"] as Record<string, unknown>)["includePerCore"]).toBe(false);
+    expect(t["group"]).toBe("default");
+    expect(t["intervalMs"]).toBe(30000);
+    expect(t["timeoutMs"]).toBe(10000);
+  });
+
+  test("解析 cpu expect 配置", async () => {
+    const configPath = join(tempDir, "cpu-expect.yaml");
+    await writeFile(
+      configPath,
+      `targets:
+  - id: "local-cpu"
+    type: cpu
+    cpu:
+      sampleDuration: "2s"
+      includePerCore: true
+    expect:
+      usagePercent: { lte: 85 }
+      idlePercent: { gte: 15 }
+      maxCoreUsagePercent: { lte: 95 }
+      durationMs: { lte: 3000 }
+`,
+    );
+
+    const config = await loadConfig(configPath);
+    expect(config.targets).toHaveLength(1);
+    const t = config.targets[0]! as Record<string, unknown>;
+    expect((t["cpu"] as Record<string, unknown>)["sampleDurationMs"]).toBe(2000);
+    expect((t["cpu"] as Record<string, unknown>)["includePerCore"]).toBe(true);
+    expect((t["expect"] as Record<string, unknown>)["usagePercent"]).toEqual({ lte: 85 });
+  });
+
+  test("cpu expect 未知字段抛出错误", async () => {
+    await expectConfigError(
+      "cpu-unknown-expect.yaml",
+      `targets:
+  - id: "local-cpu"
+    type: cpu
+    cpu: {}
+    expect:
+      logicalCoreCount: { gte: 4 }
+`,
+      "expect.logicalCoreCount 是未知字段",
+    );
+  });
+
+  test("cpu sampleDuration >= timeout 抛出错误", async () => {
+    await expectConfigError(
+      "cpu-sample-too-long.yaml",
+      `targets:
+  - id: "local-cpu"
+    type: cpu
+    timeout: "1s"
+    cpu:
+      sampleDuration: "5s"
+`,
+      "sampleDuration 必须小于 timeout",
+    );
+  });
+
   describe("logging 配置", () => {
     test("logging 全部缺省时使用默认值", async () => {
       const configPath = join(tempDir, "logging-default.yaml");