Convert a Space into a folder in another Space (like Arc)

[peter-neumann-dev]

Idea

Add a "Convert to folder" action to the Space context menu. It moves the contents of a Space into a new folder in another Space and then deletes the empty Space.

Arc had this. When a Space no longer needed its own spot in the sidebar, a right-click turned it into a folder inside another Space.

Proposed behavior

1. Right-click a Space icon and pick "Convert to folder in", then the target Space.
2. Zen creates a folder in the target Space with the old Space's name and icon.
3. Pinned tabs go into the new folder, and existing folders become subfolders. Unpinned tabs move to the target Space's regular tab list.
4. Zen deletes the empty source Space.

The reverse action, turning a folder into its own Space, would fit next to it.

Why

Today this takes several manual steps:

1. Create a folder in the target Space.
2. Select all tabs in the old Space and move them to the target Space.
3. Drag them into the folder.
4. Delete the old Space.

Related

#10051 asks for merging Spaces into one. This request keeps the old Space's tabs grouped as a folder instead of mixing them into the target Space.