rega's :dir(rtl) mirror for VerticalTabsLayout (5e7f73d0) compiled into
the studio, but nothing set the direction, so the studio stayed
left-to-right in Arabic. The studio now sets dir from the language
list's own dir flag, as doxa-maps-spa does.
The Explorer tree's own CSS assumed left-to-right: indentation, indent
guides, the active-row bar, the part count and the slim-rail activity
icons used left/right properties. They now use logical properties
(padding-inline, inset-inline-start, border-inline-start,
margin-inline-start), so they mirror, and a closed twisty points toward
the start of the line.
Checked at 1280x900: in Arabic the rail sits on the right, the active
bar on its right edge, the guides on the right, and doxa-simple-map
still renders its map; in English the geometry is unchanged (rail 0..256,
stage from 268).
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