fix: avatar picker uses chooseMedia, COS domain to tx.vsai.net.cn

- Replace chooseAvatar button with chooseMedia (more reliable, works on all versions)
- COS avatar URL uses tx.vsai.net.cn instead of generated bucket domain
- Phone shows '已授权' only (no actual number displayed)

miniprogram/pages/register/register.js

@@ -28,10 +28,18 @@ Page({
     })
   },
 
-  onChooseAvatar: function (e) {
-    if (e.detail && e.detail.avatarUrl) {
-      this.setData({ avatarUrl: e.detail.avatarUrl })
-    }
+  onPickAvatar: function () {
+    var self = this
+    wx.chooseMedia({
+      count: 1,
+      mediaType: ['image'],
+      sourceType: ['album', 'camera'],
+      success: function (res) {
+        if (res.tempFiles && res.tempFiles[0]) {
+          self.setData({ avatarUrl: res.tempFiles[0].tempFilePath })
+        }
+      }
+    })
   },
 
   onNicknameInput: function (e) {