theme: GTK and Qt take the YoRHa palette

GTK moves from Catppuccin Mocha to adw-gtk3-dark, recoloured through the
libadwaita named colours in gtk-3.0/gtk.css and as CSS variables in
gtk-4.0/gtk.css, so Nautilus and other libadwaita apps follow too. The
gtk-4.0 symlinks into the Catppuccin theme are gone, since libadwaita
would load its gtk-dark.css over the overrides.

Qt gets qt6ct/colors/yorha.conf: the same palette in QPalette roles,
with the light slab as the highlight and ink as its text.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -44,3 +44,6 @@ gtk-4.0/*
 !qt6ct/
 qt6ct/*
 !qt6ct/qt6ct.conf
+!qt6ct/colors/
+qt6ct/colors/*
+!qt6ct/colors/yorha.conf