feat: add registration page for new miniprogram users

- New register page with chooseAvatar, nickname input (random default),
  and required phone number authorization via getPhoneNumber
- Login simplified: removed deprecated wx.getUserProfile, checks
  is_new_user flag to redirect new users to registration
- Server login response now includes is_new_user field

miniprogram/pages/login/login.wxml

@@ -1,7 +1,7 @@
 <view class="page">
   <view class="page-header page-header-pink" style="padding-top: {{statusBarHeight + 24}}px;">
     <view class="page-header-title">光子美容仪</view>
-    <view class="page-header-subtitle">微信授权登录</view>
+    <view class="page-header-subtitle">微信登录</view>
   </view>
 
   <view class="page-content">
@@ -9,17 +9,11 @@
 
     <view class="flower-area">
       <text class="flower">🌸</text>
-      <view class="desc">授权获取微信昵称和头像</view>
-      <view class="desc">用于完善会员资料</view>
+      <view class="desc">登录后即可使用全部功能</view>
     </view>
 
     <button class="login-btn" loading="{{loading}}" bindtap="onLogin" disabled="{{loading}}">
-      微信授权登录
-    </button>
-
-    <!-- 手机号授权已预留。需要时展示该按钮并隐藏上面的普通登录按钮。 -->
-    <button wx:if="{{false}}" class="phone-btn disabled-phone-btn" open-type="getPhoneNumber" bindgetphonenumber="onGetPhoneNumber" disabled="{{loading}}">
-      授权手机号登录（预留）
+      微信登录
     </button>
 
     <view class="agreement" bindtap="onAgreement">登录即表示同意《用户协议》和《隐私政策》</view>