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/shared/value-matcher-shorthand.test.ts

@@ -40,9 +40,9 @@ describe("ValueMatcher primitive shorthand in checker validators", () => {
       },
       {
         expect: { avgLatencyMs: 1, durationMs: 100, maxLatencyMs: 2, packetLossPercent: 0 },
-        id: "ping",
-        ping: { host: "127.0.0.1" },
-        type: "ping",
+        icmp: { host: "127.0.0.1" },
+        id: "icmp",
+        type: "icmp",
         validate: validatePingConfig,
       },
       {