Split ISO config from installed hosts; auto-include gnome in generated host

hosts/iso.nix

@@ -0,0 +1,25 @@
+{ config, pkgs, inputs, ... }:
+
+# ISO-only configuration (uses installation-cd profile). Do not use for installed systems.
+{
+  imports = [
+    (inputs.nixpkgs + "/nixos/modules/installer/cd-dvd/installation-cd-minimal.nix")
+    inputs.lix-module.nixosModules.lixFromNixpkgs
+    ../modules/system/base.nix
+    ../modules/desktop/gnome-minimal.nix
+    ../modules/users/admin.nix
+  ];
+
+  networking.hostName = "iso-installer";
+
+  environment.etc."INSTALL.txt".source = ../docs/install-help.txt;
+  environment.etc."motd".text = builtins.readFile ../docs/install-help.txt;
+  environment.etc."issue".text = ''
+${builtins.readFile ../docs/install-help.txt}
+
+Login: \l
+  '';
+
+  # Embed the repo in the live ISO.
+  environment.etc."nixos".source = ../.;
+}