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

server/src/routes/auth.js

@@ -16,7 +16,9 @@ router.post('/auth/login', wrap(async (req, res) => {
 
   const session = await code2Session(req.body.code || '')
   let user = await userDao.findByOpenid(session.openid)
+  let isNewUser = false
   if (!user) {
+    isNewUser = true
     const result = await userDao.create(session.openid)
     user = await userDao.findById(result.insertId)
     await logDao.write({ user_id: user.user_id, action: 'user_register', detail: '新用户注册', ip: req.ip })
@@ -26,6 +28,7 @@ router.post('/auth/login', wrap(async (req, res) => {
   res.json(ok({
     token,
     user_id: String(user.user_id),
+    is_new_user: isNewUser,
     user_info: {
       user_id: String(user.user_id),
       nickname: user.nickname || '用户' + String(user.user_id),