fix: 退出登录时保留deviceId

- logout时先保存deviceId，清除缓存后恢复
- 确保同一设备退出登录后再次登录不会创建新用户

xuan-deduct-uniapp/src/pages/mine/account.vue

@@ -135,7 +135,11 @@ export default {
         content: '确定要退出登录吗？',
         success: (res) => {
           if (res.confirm) {
+            const deviceId = uni.getStorageSync('deviceId')
             uni.clearStorageSync()
+            if (deviceId) {
+              uni.setStorageSync('deviceId', deviceId)
+            }
             uni.setStorageSync('isLoggedIn', false)
             uni.showToast({
               title: '已退出登录',