Xios desktop defaults

Installs the ambient desktop defaults for the Xios X11 environment.

It sets up Xios shell and XDG environment defaults, native iPad retina display profiles, Xft antialiasing and DPI resources, GTK3/GTK4 settings, UTF-8 locale defaults, touch-friendly cursor sizing, and runtime directories used by X11/GTK/Xfce/GNOME apps.

• Native profile: 2160x1620 at 264 DPI
• Comfy profile: 1440x1080 at 176 DPI
• Debug/VNC profile: 1024x768 at 96 DPI
• Ships a minimal real hicolor icon-theme index, so the GTK icon theme setting points at something installed
• Refreshes fontconfig, GSettings schemas, icon, MIME, and desktop databases when the relevant tools are present