Switch to GNOME and Limine bootloader

Migrates the NixOS system to use GNOME as the primary desktop environment and Limine as the bootloader.

This involves removing the KDE Plasma configuration module and adding a dedicated module for Limine. Also includes a minor cleanup in the Darwin home-manager configuration.

hosts/nixos/system/os.nix

@@ -2,7 +2,7 @@
 
 {
   # System services
-  os.boot.systemd.enable = true;
+  os.boot.limine.enable = true;
   os.boot.plymouth.enable = true;
   os.graphics.nvidia.enable = true;
   os.audio.pipewire.enable = true;
@@ -25,7 +25,7 @@
   os.virtualisation.podman.enable = true;
 
   # Shells configurations
-  os.shells.kde.enable = true;
+  os.shells.gnome.enable = true;
 
   # Terminal
   programs.ssh.enableAskPassword = false; # No-window git push fix