Re-approve the native captures for the fold markers

The queue column gained a marker per header and two more columns of indent
on its entries, so every capture with a group in it moves. Three of them:
the grouped queue on both native heads, and the Linux context menu, whose
queue is behind the menu it is really about.

The Linux head also draws its headers as Selectables now, which a capture
cannot tell apart -- it feeds no mouse, so nothing hovers.

Author: SimonCropp