The "Unset" toggle button next to the color picker used a custom
HashSwatch drawing area that mirrored the canvas's diagonal-hash
pattern for unset cells. The pattern was visually noisy at button
size and tied the button's appearance to the current zone base
color (the swatch had to be told the base color via
set_zone_base_color so it could redraw).
Use the Tabler "palette-off" symbolic icon instead. It reads as
"clear / no paint" at a glance, is independent of the zone base
color, and matches the icon style of the tool buttons on the other
end of the toolbar.
Extract the icon loader (themed_icon_image, ensure_icon_path) from
editor.py into a new private module _icons.py so palette.py can
reuse it; the new palette tracks its own Gtk.Settings notify signals
to re-render the icon on theme switches, and disconnects them via a
new Palette.shutdown() called from the editor's shutdown.
Adds MIT-licensed Tabler palette-off icon under share/solaar/icons/,
see THIRD_PARTY.md.
The Brush / Rect / Fill tool buttons in the per-key color editor now
show icons instead of text labels, with the original labels retained
as tooltips and accessible names.
Icons are recolored at load time to match the active GTK theme's text
foreground (light grey on dark themes, dark on light), by reading the
button's style context and substituting currentColor in the SVG before
loading the pixbuf. GTK's stock symbolic loader is bypassed because it
only recolors fill palette stand-ins and ignores stroke="currentColor",
which is what the source SVGs use.
Adds MIT-licensed Tabler icons under share/solaar/icons/, see
THIRD_PARTY.md.