- Move the expand chevron into a gutter left of the folder icon so folders
with and without subfolders line up on their icon; labels share the column.
- Add "Mark all as read, incl. subfolders" to the folder context menu, with
the affected count and a per-folder fallback for servers without filter
operators.
- Re-measure the virtualised message list when row height changes.
- Mock: seed unread mail in a subfolder.
The LICENSE file only carried the short "how to apply" notice, not the
license itself, so it wasn't a valid GPLv3 distribution and license
detection tools couldn't identify it. Replace it with the canonical
674-line GNU GPL v3 text (sha256 8ceb4b9e...), and move the project
copyright line plus the "version 3 or any later version" grant into the
README, which now matches package.json's GPL-3.0-or-later.