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>

gtk-3.0/settings.ini

@@ -1,5 +1,5 @@
 [Settings]
-gtk-theme-name=catppuccin-mocha-blue-standard+default
+gtk-theme-name=adw-gtk3-dark
 gtk-icon-theme-name=Papirus-Dark
 gtk-font-name=Adwaita Sans 11
 gtk-cursor-theme-name=Bibata-Modern-Classic