余额告警独立页面与多渠道通知：钉钉/飞书/企业微信/Bark，支持通知频率策略

- 告警设置拆分为独立页面，支持钉钉/飞书/企业微信/Bark/通用Webhook 多渠道
- 通知策略：低于阈值后按间隔重复提醒，达到最大次数停止，余额恢复自动重置
- 旧 webhook 配置自动迁移为通用渠道，渠道支持测试发送
- 优化告警话术：去商户ID展示、数字千分位格式化

frontend/src/api/index.ts

@@ -1,6 +1,8 @@
 import request from './request'
 import type {
   DashboardStats,
+  AlertChannelInput,
+  AlertNotifyChannel,
   ApiClient,
   ApiCredential,
   CallbackCredential,
@@ -108,8 +110,18 @@ export const merchantApi = {
     request.post('/merchant/recharge/applications', data).then((r) => r.data.data as RechargeApplication),
   alertConfig: () =>
     request.get('/merchant/recharge/alert-config').then((r) => r.data.data as LowBalanceAlertConfig),
-  saveAlertConfig: (data: LowBalanceAlertConfig) =>
+  saveAlertConfig: (data: { enabled: boolean; threshold_points: number; notify_interval_minutes: number; max_notifications: number }) =>
     request.put('/merchant/recharge/alert-config', data).then((r) => r.data.data as LowBalanceAlertConfig),
+  alertChannels: () =>
+    request.get('/merchant/alert-channels').then((r) => r.data.data as AlertNotifyChannel[]),
+  createAlertChannel: (data: AlertChannelInput) =>
+    request.post('/merchant/alert-channels', data).then((r) => r.data.data as AlertNotifyChannel),
+  updateAlertChannel: (id: number, data: AlertChannelInput) =>
+    request.put(`/merchant/alert-channels/${id}`, data).then((r) => r.data.data as AlertNotifyChannel),
+  deleteAlertChannel: (id: number) =>
+    request.delete(`/merchant/alert-channels/${id}`).then((r) => r.data.data),
+  testAlertChannel: (id: number) =>
+    request.post(`/merchant/alert-channels/${id}/test`).then((r) => r.data.data),
 }
 
 export const uploadApi = {