GDM's greeter requires gnome-session-x11@gnome-login.target (from
gnome-shell), which isn't installed on i3-only setups. This caused
gnome-session to crash-loop, leaving a blank screen on boot.
LightDM works without gnome-shell and is a better fit for i3.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
services.xserver.enable = true was dropped when desktop.nix was split
into desktop-light.nix, causing vade and orion to boot to a blank
screen with no X11/GDM session.
