feat(payment): add complete payment system with multi-provider support

Add a full payment and subscription system supporting EasyPay (Alipay/WeChat),
Stripe, and direct Alipay/WeChat Pay providers with multi-instance load balancing.

frontend/src/api/admin/index.ts

@@ -26,6 +26,7 @@ import scheduledTestsAPI from './scheduledTests'
 import backupAPI from './backup'
 import tlsFingerprintProfileAPI from './tlsFingerprintProfile'
 import channelsAPI from './channels'
+import adminPaymentAPI from './payment'
 
 /**
  * Unified admin API object for convenient access
@@ -53,7 +54,8 @@ export const adminAPI = {
   scheduledTests: scheduledTestsAPI,
   backup: backupAPI,
   tlsFingerprintProfiles: tlsFingerprintProfileAPI,
-  channels: channelsAPI
+  channels: channelsAPI,
+  payment: adminPaymentAPI
 }
 
 export {
@@ -79,7 +81,8 @@ export {
   scheduledTestsAPI,
   backupAPI,
   tlsFingerprintProfileAPI,
-  channelsAPI
+  channelsAPI,
+  adminPaymentAPI
 }
 
 export default adminAPI