refactor: ICMP checker type 从 ping 统一改为 icmp，修复前端 UI 细节

- ICMP checker 的 type/configKey/YAML 配置键/接口属性名从 ping 改为 icmp
- IcmpChecker 添加 platform 构造函数注入，修复 Windows 测试兼容性
- 前端 target 表格延迟列优化：标题简化为「延迟」，单位下移到单元格，宽度 80px
- Drawer 概览页 Descriptions 添加 tableLayout=auto 收窄 label 宽度
- 同步更新 README.md、DEVELOPMENT.md、probes.example.yaml、JSON Schema 和全部测试

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

@@ -8,12 +8,12 @@ function makeTarget(overrides?: Partial<ResolvedPingTarget>): ResolvedPingTarget
   return {
     description: null,
     group: "default",
+    icmp: { count: 3, host: "10.0.0.1", packetSize: 56 },
     id: "test",
     intervalMs: 30000,
     name: null,
-    ping: { count: 3, host: "10.0.0.1", packetSize: 56 },
     timeoutMs: 10000,
-    type: "ping",
+    type: "icmp",
     ...overrides,
   };
 }
@@ -46,7 +46,7 @@ describe("buildPingCommand", () => {
 
   test("自定义 count 和 packetSize", () => {
     const cmd = buildPingCommand(
-      makeTarget({ ping: { count: 5, host: "10.0.0.1", packetSize: 1472 }, timeoutMs: 5000 }),
+      makeTarget({ icmp: { 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"]);