feat(gateway): 网关健康状态——后台定时探活只保留最近一次结果并在列表展示

- 迁移 1043：gateway 表加 health_status/last_check_reason/last_checked_at
- Store.RecordGatewayCheck 覆盖写最近一次探活结果，Create/Update/List/Get 全量返回健康字段
- api.RecordGatewayHealthChecks 并发探 /healthz：连接失败或 5xx 判离线，其余判在线（401 等异常写入原因供排查）
- workers 每 30 秒一轮，app 启动接线
- 网关管理列表新增健康状态列：在线/离线/未检查 Tag，原因与检查时间收进 Tooltip

web/src/pages/gateways/index.tsx

@@ -1,15 +1,30 @@
 // 网关管理：语义对齐 web.archived GatewaysPage.jsx（注册/编辑 Modal、令牌显隐复制、删除）。
 import { useCallback, useEffect, useState } from 'react';
-import { Alert, App, Button, Card, Flex, Form, Input, Modal, Popconfirm, Space, Table, Typography } from 'antd';
+import { Alert, App, Button, Card, Flex, Form, Input, Modal, Popconfirm, Space, Table, Tag, Tooltip, Typography } from 'antd';
 import { CopyOutlined, EyeInvisibleOutlined, EyeOutlined, PlusOutlined } from '@ant-design/icons';
 import type { ColumnsType } from 'antd/es/table';
 import { create, getList, remove, update } from '@/services/api';
-import { conflictMessage } from '@/utils/helpers';
+import { conflictMessage, dateTime } from '@/utils/helpers';
 import { fixedLeft, fixedRight, tablePagination, tableScroll, useOverflowGrid } from '@/utils/table';
 
 const namePattern = /^[A-Za-z0-9][A-Za-z0-9._-]{0,63}$/;
 const tokenPattern = /^[A-Za-z0-9][A-Za-z0-9._-]{15,127}$/;
 
+// 健康状态列：只展示后台定时探活的最近一次结果，不保留历史。
+function HealthCell({ status, reason, checkedAt }: { status?: string; reason?: string; checkedAt?: string }) {
+  const label = status === 'healthy' ? '在线' : status === 'unhealthy' ? '离线' : '未检查';
+  const color = status === 'healthy' ? 'success' : status === 'unhealthy' ? 'error' : 'default';
+  const details = [
+    checkedAt ? `最近检查：${dateTime(checkedAt)}` : null,
+    reason || null,
+  ].filter(Boolean).join('；');
+  return (
+    <Tooltip title={details || '尚未执行健康检查'}>
+      <Tag color={color}>{label}</Tag>
+    </Tooltip>
+  );
+}
+
 function GatewayFormModal({
   open,
   initial,
@@ -146,6 +161,12 @@ export default function Page() {
   const columns: ColumnsType<any> = [
     { title: '名称', dataIndex: 'name', ...fixedLeft<any>({}), render: (value: string) => <Typography.Text strong>{value}</Typography.Text> },
     { title: 'Endpoint', dataIndex: 'endpoint', render: (value: string) => <Typography.Text code style={{ fontSize: 12 }} ellipsis>{value}</Typography.Text> },
+    {
+      title: '健康状态',
+      dataIndex: 'health_status',
+      width: 110,
+      render: (_, gateway) => <HealthCell status={gateway.health_status} reason={gateway.last_check_reason} checkedAt={gateway.last_checked_at} />,
+    },
     {
       title: '令牌',
       dataIndex: 'token',