[FEAT] support "delve" UI mode

### Is your feature request related to a problem? / 你想要的功能和什么问题相关？

It would be useful to create conversation trees instead of only being able to create lists. This may be a limitation of the underlying AI platforms. Inspiration: https://news.ycombinator.com/item?id=40522844

### Describe the solution you'd like. / 你想要的解决方案是什么？

I want to be able to fork my AI conversation into trees and not be limited only to lists.

### Describe alternatives you've considered. / 你考虑过的其他方案是什么？

_No response_

### Additional context / 其他信息

_No response_