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/command.test.ts

@@ -0,0 +1,54 @@
+import { describe, expect, test } from "bun:test";
+
+import type { ResolvedPingTarget } from "../../../../../src/server/checker/runner/icmp/types";
+
+import { buildPingCommand } from "../../../../../src/server/checker/runner/icmp/command";
+
+function makeTarget(overrides?: Partial<ResolvedPingTarget>): ResolvedPingTarget {
+  return {
+    description: null,
+    group: "default",
+    id: "test",
+    intervalMs: 30000,
+    name: null,
+    ping: { count: 3, host: "10.0.0.1", packetSize: 56 },
+    timeoutMs: 10000,
+    type: "ping",
+    ...overrides,
+  };
+}
+
+describe("buildPingCommand", () => {
+  test("Linux 默认参数", () => {
+    const cmd = buildPingCommand(makeTarget(), "linux");
+    expect(cmd).toEqual(["ping", "-c", "3", "-s", "56", "-W", "10", "10.0.0.1"]);
+  });
+
+  test("Linux 秒向上取整", () => {
+    const cmd = buildPingCommand(makeTarget({ timeoutMs: 10500 }), "linux");
+    expect(cmd[6]).toBe("11");
+  });
+
+  test("Linux timeoutMs < 1000 向上取整为 1", () => {
+    const cmd = buildPingCommand(makeTarget({ timeoutMs: 500 }), "linux");
+    expect(cmd[6]).toBe("1");
+  });
+
+  test("macOS 毫秒", () => {
+    const cmd = buildPingCommand(makeTarget(), "darwin");
+    expect(cmd).toEqual(["ping", "-c", "3", "-s", "56", "-W", "10000", "10.0.0.1"]);
+  });
+
+  test("Windows 格式", () => {
+    const cmd = buildPingCommand(makeTarget(), "win32");
+    expect(cmd).toEqual(["ping", "-n", "3", "-l", "56", "-w", "10000", "10.0.0.1"]);
+  });
+
+  test("自定义 count 和 packetSize", () => {
+    const cmd = buildPingCommand(
+      makeTarget({ ping: { count: 5, host: "10.0.0.1", packetSize: 1472 }, timeoutMs: 5000 }),
+      "linux",
+    );
+    expect(cmd).toEqual(["ping", "-c", "5", "-s", "1472", "-W", "5", "10.0.0.1"]);
+  });
+});