feat(virtualisation): update libvirtd enablement logic

- Disable libvirtd explicitly in m4nix configuration.
- Use `lib.mkDefault` for libvirtd enablement in base services to allow overrides.

modules/nixos/services/base/default.nix

@@ -186,7 +186,7 @@ in
       };
     };
 
-    virtualisation.libvirtd.enable = true;
+    virtualisation.libvirtd.enable = lib.mkDefault true;
 
     boot.tmp.useTmpfs = true;
     systemd.services.nix-daemon.environment.TMPDIR = "/var/tmp";

systems/aarch64-linux/m4nix/default.nix

@@ -63,6 +63,7 @@ with lib.metacfg;
   virtualisation = {
     docker.enable = true;
     podman.dockerCompat = false;
+    libvirtd.enable = false;
   };
 
   system.autoUpgrade = {