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/runner/cpu/normalize.test.ts

@@ -0,0 +1,41 @@
+import { describe, expect, test } from "bun:test";
+
+import { normalizeTargetExpect } from "../../../../../src/server/checker/runner/cpu/normalize";
+
+describe("normalizeTargetExpect (cpu)", () => {
+  test("无 expect 直接返回", () => {
+    const target = { cpu: {}, id: "test", type: "cpu" };
+    expect(normalizeTargetExpect(target)).toEqual(target);
+  });
+
+  test("expect 为非对象直接返回", () => {
+    const target = { cpu: {}, expect: "not-an-object", id: "test", type: "cpu" };
+    expect(normalizeTargetExpect(target)).toEqual(target);
+  });
+
+  test("ValueMatcher 简写展开", () => {
+    const target = { cpu: {}, expect: { usagePercent: 85 }, id: "test", type: "cpu" };
+    const result = normalizeTargetExpect(target);
+    expect((result.expect as Record<string, unknown>)["usagePercent"]).toEqual({ equals: 85 });
+  });
+
+  test("已经是 matcher 对象的不变", () => {
+    const target = { cpu: {}, expect: { usagePercent: { lte: 85 } }, id: "test", type: "cpu" };
+    const result = normalizeTargetExpect(target);
+    expect((result.expect as Record<string, unknown>)["usagePercent"]).toEqual({ lte: 85 });
+  });
+
+  test("多个字段同时展开", () => {
+    const target = {
+      cpu: {},
+      expect: { idlePercent: 15, maxCoreUsagePercent: { lte: 95 }, usagePercent: 85 },
+      id: "test",
+      type: "cpu",
+    };
+    const result = normalizeTargetExpect(target);
+    const expectObj = result.expect as Record<string, unknown>;
+    expect(expectObj["idlePercent"]).toEqual({ equals: 15 });
+    expect(expectObj["maxCoreUsagePercent"]).toEqual({ lte: 95 });
+    expect(expectObj["usagePercent"]).toEqual({ equals: 85 });
+  });
+});