feat: test overlay and 'base' role

hosts/NixOS-VM/default.nix

@@ -9,6 +9,8 @@
     "${modulesPath}/virtualisation/qemu-vm.nix"
   ];
 
+  ataraxia.defaults.role = "base";
+
   virtualisation.memorySize = 4096;
   virtualisation.cores = 4;
   virtualisation.resolution.x = 1920;
@@ -30,5 +32,10 @@
   boot.zfs.forceImportRoot = false;
   networking.hostId = "84977205";
 
+  environment.systemPackages = with pkgs; [
+    # test overlay
+    sing-box
+  ];
+
   system.stateVersion = "24.11";
 }