fix: Replace the question flow with a menu that turns components on and off

- Menu detects what is on and applies only the changes: SteamOS
  conversion, SteamOS theme, Steam Deck/Machine icons, single user mode,
  and Steam Machine support (only on Fremont hardware)
- Everything is reversible: KDE settings go through an undo journal
  (lib/state.sh), system files are restored from their backups
- Steam Machine support: LED driver, udev rule giving the user the LED
  files, steamos-manager for Steam's hardware settings; OpenRGB dropped
- Edit Plasma files only while plasmashell is stopped so it can't
  overwrite them
- README and AGENTS.md describe the menu, the component model and the
  test environment

lib/desktop-shortcut.sh

@@ -68,3 +68,10 @@ EOF
 
     ok "Desktop shortcut created successfully."
 }
+
+remove_desktop_shortcut() {
+    local desktop_dir
+    desktop_dir="$(xdg-user-dir DESKTOP 2>/dev/null || echo "$HOME/Desktop")"
+    rm -f "$desktop_dir/Return to Gaming Mode.desktop"
+    sudo rm -f /etc/sudoers.d/gamescope-session-switch
+}