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/parse.test.ts

@@ -0,0 +1,61 @@
+import { describe, expect, test } from "bun:test";
+
+import { parsePingOutput } from "../../../../../src/server/checker/runner/icmp/parse";
+
+describe("parsePingOutput", () => {
+  test("解析 Linux ping 输出", () => {
+    const stats = parsePingOutput(
+      `3 packets transmitted, 3 received, 0% packet loss, time 2003ms
+rtt min/avg/max/mdev = 1.234/2.345/3.456/0.567 ms`,
+      "linux",
+    );
+    expect(stats).toEqual({
+      alive: true,
+      avgLatencyMs: 2.345,
+      maxLatencyMs: 3.456,
+      minLatencyMs: 1.234,
+      packetLoss: 0,
+      received: 3,
+      transmitted: 3,
+    });
+  });
+
+  test("解析 macOS ping 输出", () => {
+    const stats = parsePingOutput(
+      `3 packets transmitted, 3 packets received, 0.0% packet loss
+round-trip min/avg/max/stddev = 1.234/2.345/3.456/0.567 ms`,
+      "darwin",
+    );
+    expect(stats?.avgLatencyMs).toBe(2.345);
+    expect(stats?.packetLoss).toBe(0);
+  });
+
+  test("解析 Windows 英文 ping 输出", () => {
+    const stats = parsePingOutput(
+      `Packets: Sent = 3, Received = 3, Lost = 0 (0% loss),
+Approximate round trip times in milli-seconds:
+    Minimum = 1ms, Maximum = 3ms, Average = 2ms`,
+      "win32",
+    );
+    expect(stats).toMatchObject({ avgLatencyMs: 2, maxLatencyMs: 3, minLatencyMs: 1, packetLoss: 0 });
+  });
+
+  test("解析 Windows 中文 ping 输出", () => {
+    const stats = parsePingOutput(
+      `数据包: 已发送 = 3，已接收 = 3，丢失 = 0 (0% 丢失)，
+往返行程的估计时间(以毫秒为单位):
+    最短 = 1ms，最长 = 3ms，平均 = 2ms`,
+      "win32",
+    );
+    expect(stats).toMatchObject({ avgLatencyMs: 2, maxLatencyMs: 3, minLatencyMs: 1, packetLoss: 0 });
+  });
+
+  test("解析全部丢包", () => {
+    const stats = parsePingOutput(`3 packets transmitted, 0 received, 100% packet loss, time 2003ms`, "linux");
+    expect(stats).toMatchObject({ alive: false, avgLatencyMs: null, maxLatencyMs: null, minLatencyMs: null });
+  });
+
+  test("无法解析返回 null", () => {
+    expect(parsePingOutput("unexpected output", "linux")).toBeNull();
+  });
+});