fix: serverless adapter binary body support, hide phone number in register

- Keep body as Buffer instead of utf8 string for multipart/form-data
- Set content-length header for multer compatibility
- Phone authorization shows '已授权' instead of actual number

miniprogram/pages/register/register.js

@@ -57,7 +57,7 @@ Page({
     http.post('/api/v1/user/phone', { code: e.detail.code }).then(function (data) {
       self.setData({
         loading: false,
-        phone: data.phone || data.pure_phone_number || '已授权'
+        phone: '已授权'
       })
       wx.showToast({ title: '手机号授权成功', icon: 'success' })
     }).catch(function (err) {