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/register/register.wxml

@@ -0,0 +1,43 @@
+<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">完善个人资料</view>
+  </view>
+
+  <view class="page-content">
+    <view class="section-title">设置头像</view>
+    <view class="avatar-area">
+      <button class="avatar-btn" open-type="chooseAvatar" bindchooseavatar="onChooseAvatar">
+        <image class="avatar-img" src="{{avatarUrl}}" mode="aspectFill"></image>
+        <view class="avatar-edit-hint">点击更换</view>
+      </button>
+    </view>
+
+    <view class="section-title">设置昵称</view>
+    <view class="input-wrap">
+      <input type="nickname" class="weui-input nickname-input" value="{{nickname}}" bindinput="onNicknameInput" bindblur="onNicknameBlur" placeholder="请输入昵称" />
+    </view>
+
+    <view class="section-title">授权手机号</view>
+    <view class="phone-area">
+      <block wx:if="{{phone}}">
+        <view class="phone-done">
+          <text class="phone-icon">&#x2713;</text>
+          <text class="phone-text">{{phone}}</text>
+        </view>
+      </block>
+      <block wx:else>
+        <button class="phone-btn" open-type="getPhoneNumber" bindgetphonenumber="onGetPhoneNumber" disabled="{{loading}}">
+          授权手机号
+        </button>
+        <view class="phone-hint">手机号用于接收服务通知，必须授权</view>
+      </block>
+    </view>
+
+    <button class="submit-btn" bindtap="onSubmit" loading="{{loading}}" disabled="{{loading}}">
+      完成注册
+    </button>
+
+    <view class="agreement" bindtap="onAgreement">注册即表示同意《用户协议》和《隐私政策》</view>
+  </view>
+</view>