Folders for worldbuilding pages

A lot of people have asked for folders (and/or nesting pages under other pages) over the years. Now that we have page tags (which function very similar to folders) and we're considering document folders (#332), we should figure out how page folders should fit into Notebook.ai.

* Should tags be expanded to also function like (and look more like) folders?
* Should folders exist alongside tags? What makes the two different?
* Should pages be able to nest under other pages? (Perhaps this is unrelated to folders though)

Opening this issue as a placeholder to dump feedback and request commentary. 👍

Start by reviewing the six comments and the related document-folders issue (#332). Clarify whether tags should serve as folders, whether folders should coexist with tags, and whether pages should nest. Define the product direction and implementation scope before identifying code or tests.

Written by the indexing model from the issue text.