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

src/web/components/OverviewTab.tsx

@@ -40,6 +40,7 @@ export function OverviewTab({ metricsData, metricsLoading, target }: OverviewTab
           { content: target.latestCheck?.detail ?? "-", label: "状态详情" },
           { content: target.description ?? "", label: "描述", span: 2 },
         ]}
+        tableLayout="auto"
       />
 
       <Divider align="left">统计</Divider>

src/web/constants/target-table-columns.tsx

@@ -89,13 +89,13 @@ export function createTargetTableColumns(checkerTypes: string[]): Array<PrimaryT
         if (ms === null || ms === undefined) return <span className="text-disabled">-</span>;
         const colorClass = ms <= 100 ? "latency-ok" : ms <= 500 ? "latency-warn" : "latency-error";
         const latencyText = ms > 9999 ? "9999+" : `${Math.round(ms)}`;
-        return <span className={`${colorClass} latency-value tabular-nums`}>{latencyText}</span>;
+        return <span className={`${colorClass} latency-value tabular-nums`}>{latencyText} ms</span>;
       },
       colKey: "latestCheck.durationMs",
       sorter: latencySorter,
       sortType: "all",
-      title: "延迟(ms)",
-      width: 75,
+      title: "延迟",
+      width: 80,
     },
   ];
 }