feat: add auto-increment userId (8-digit padded) to User model and login response

src/models/User.js

@@ -12,6 +12,11 @@ const userSchema = new mongoose.Schema({
     sparse: true,
     index: true
   },
+  userId: {
+    type: String,
+    unique: true,
+    index: true
+  },
   nickname: {
     type: String,
     default: ''

src/routes/auth.js

@@ -4,6 +4,23 @@ const axios = require('axios');
 const jwt = require('jsonwebtoken');
 const User = require('../models/User');
 
+async function generateUserId() {
+  const lastUser = await User.findOne({ userId: { $exists: true } })
+    .sort({ userId: -1 })
+    .select('userId')
+    .lean();
+  
+  let nextNumber = 1;
+  if (lastUser && lastUser.userId) {
+    const lastNumber = parseInt(lastUser.userId, 10);
+    if (!isNaN(lastNumber)) {
+      nextNumber = lastNumber + 1;
+    }
+  }
+  
+  return nextNumber.toString().padStart(8, '0');
+}
+
 router.post('/wechat-login', async (req, res, next) => {
   try {
     const { code, userInfo } = req.body;
@@ -40,9 +57,12 @@ router.post('/wechat-login', async (req, res, next) => {
     let user = await User.findOne({ openid });
 
     if (!user) {
+      const userId = await generateUserId();
+      
       user = await User.create({
         openid,
         unionid: unionid || undefined,
+        userId,
         nickname: userInfo?.nickName || '',
         avatarUrl: userInfo?.avatarUrl || '',
         profile: {
@@ -72,7 +92,7 @@ router.post('/wechat-login', async (req, res, next) => {
       data: {
         token,
         user: {
-          id: user._id,
+          userId: user.userId,
           nickname: user.nickname,
           avatarUrl: user.avatarUrl,
           status: user.status,