Improve the display logic for mobile indent and outdent button

只显示反缩进按钮，隐藏缩进按钮。

目前会误导用户：

<img width="917" height="676" alt="Image" src="https://github.com/user-attachments/assets/ec61f441-62db-4300-824f-3d2929597176" />
