modules: users: add systemType and isGraphical options

systemType describes the type of a system, e.g. a laptop,
desktop or server. 

isGraphical takes this to determine whether a system needs
programs such as a compositor, graphical applications etc.

modules/other/users.nix

@@ -7,7 +7,7 @@
 }: let
   inherit (builtins) elemAt;
   inherit (lib.options) mkOption;
-  inherit (lib.types) listOf str;
+  inherit (lib.types) listOf str package;
 
   inherit (config.meta.mainUser) username;
 in {
@@ -27,6 +27,7 @@ in {
           The main user for each system. This is the first element of the list of users by default.
         '';
       };
+
       gitSigningKey = mkOption {
         type = str;
         description = ''
@@ -36,9 +37,28 @@ in {
           ecdsa-sha2-nistp521 AAAAE2VjZHNhLXNoYTItbmlzdHA1MjEAAAAIbmlzdHA1MjEAAACFBAAWEDj/Yib6Mqs016jx7rtecWpytwfVl28eoHtPYCM9TVLq81VIHJSN37lbkc/JjiXCdIJy2Ta3A3CVV5k3Z37NbgAu23oKA2OcHQNaRTLtqWlcBf9fk9suOkP1A3NzAqzivFpBnZm3ytaXwU8LBJqxOtNqZcFVruO6fZxJtg2uE34mAw==
         '';
       };
+
+      # TODO: clean this up and move it somewhere else.
+      defaultShell = {
+        name = mkOption {
+          type = str;
+          default = "nushell";
+          description = ''
+            The default shell of a user. This is not the main system shell, but the shell used in terminals.
+          '';
+        };
+        package = mkOption {
+          type = package;
+          default = pkgs.nushell;
+        };
+      };
     };
   };
   config = {
+    programs.zsh = {
+      enable = true;
+      enableBashCompletion = true;
+    };
     users = {
       mutableUsers = true;
       users = {
@@ -53,6 +73,7 @@ in {
             "nix"
             "docker"
           ];
+          # shell = self.packages.${pkgs.stdenv.system}.fish;
           shell = pkgs.zsh;
           # hashedPasswordFile = "/etc/passwords/cr";
         };