feat(mibook): do nothing on lid close while on AC power

Ship a system-wide PowerDevil default (/etc/xdg/powerdevilrc) setting the
AC lid-close action to "do nothing" (LidAction=0). Battery behavior is left
at the default (suspend).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KbZoyXq6J8v2eqC9yn5Vcy

machines/mibook/configuration.nix

@@ -44,6 +44,14 @@
 
   services.openssh.enable = true;
 
+  # KDE (PowerDevil) power settings: do nothing on lid close while on AC power.
+  # Shipped as a system-wide default; KConfig cascades so a user's own
+  # ~/.config/powerdevilrc will override this if present.
+  environment.etc."xdg/powerdevilrc".text = ''
+    [AC][SuspendAndShutdown]
+    LidAction=0
+  '';
+
   system = {
     stateVersion = "23.05";
     autoUpgrade.enable = true;