When clicking on the Add page button, remember the current page

It is necessary to set the current page as a parent in the parent page selection field

Steps to reproduce:
- run docs instance
- auth via /auth
- go to some existing page
- click "Add new page"
- You will see that new page will be created in the "Root", but it would be much more convenient if there was a page that the user was on before

运行 docs 实例，通过 /auth 进行身份验证，打开一个现有页面，然后点击 "Add new page"，以重现当前的 Root 选择。跟踪 Add new page 流程和父页面选择，然后验证操作开始所在的页面是否被选为新页面的父页面。

由索引模型根据 Issue 内容生成。