feat: 新增 ICMP/Ping checker，支持跨平台主机存活检测与延迟监控

实现 type: ping checker，通过 Bun.spawn 调用系统 ping 命令，自行实现跨平台
输出解析器（Linux/macOS/Windows 含中文 locale），支持 alive、丢包率、延迟、
耗时等 expect 断言，复用现有 checker 架构零外部依赖。

包含完整的类型定义、TypeBox schema、语义校验、命令构建、解析、断言、执行、
注册、配置加载测试，以及 probe-config.schema.json 更新和文档更新。

审查修复：提取 buildPingCommand 为独立纯函数并补充跨平台单测，补充
maxDurationMs/maxAvgLatencyMs 类型非法和空字符串 host 边界测试用例。

变更已归档，delta specs 已同步至 main specs。

tests/server/checker/runner/icmp/expect.test.ts

@@ -0,0 +1,44 @@
+import { describe, expect, test } from "bun:test";
+
+import {
+  checkAlive,
+  checkAvgLatency,
+  checkMaxLatency,
+  checkPacketLoss,
+} from "../../../../../src/server/checker/runner/icmp/expect";
+
+describe("ping expect", () => {
+  test("alive 通过和失败", () => {
+    expect(checkAlive(true, true).matched).toBe(true);
+    const result = checkAlive(false, true);
+    expect(result.matched).toBe(false);
+    expect(result.failure?.phase).toBe("alive");
+  });
+
+  test("packetLoss 通过和失败", () => {
+    expect(checkPacketLoss(0, 10).matched).toBe(true);
+    const result = checkPacketLoss(33, 10);
+    expect(result.matched).toBe(false);
+    expect(result.failure?.phase).toBe("packetLoss");
+  });
+
+  test("avgLatency 通过和失败", () => {
+    expect(checkAvgLatency(12, 200).matched).toBe(true);
+    const result = checkAvgLatency(156, 100);
+    expect(result.matched).toBe(false);
+    expect(result.failure?.phase).toBe("avgLatency");
+  });
+
+  test("maxLatency 通过和失败", () => {
+    expect(checkMaxLatency(340, 500).matched).toBe(true);
+    const result = checkMaxLatency(340, 200);
+    expect(result.matched).toBe(false);
+    expect(result.failure?.phase).toBe("maxLatency");
+  });
+
+  test("未配置阈值默认通过", () => {
+    expect(checkPacketLoss(100, undefined).matched).toBe(true);
+    expect(checkAvgLatency(null, undefined).matched).toBe(true);
+    expect(checkMaxLatency(null, undefined).matched).toBe(true);
+  });
+});