Library folders have no ownership tracking, so folder deletion was
gated entirely behind library:delete_all - a user with
library:delete_own could create folders and delete their own files,
but the emptied folder sat there until an admin removed it.
Users with library:delete_own can now delete folders that are truly
empty: no subfolders and no files, including trashed ones - folder
deletion cascades, so removing a folder that holds another user's
trashed file would silently break trash restore. External folders
(operator-configured mounts) and folders linked to a project or
archive still require library:delete_all even when empty, since
deleting them affects more than the folder itself. The bulk-delete
endpoint applies the same rule instead of skipping all folders for
non-admin users.
The folder tree's Delete entry enables accordingly and shows a
"You can only delete empty folders" hint on non-empty folders. The
backend stays authoritative - a folder that only contains trashed
files is invisible in the tree but still refuses deletion.