feat: simplify flake.nix

hosts/harmonica/default.nix

@@ -1,25 +1,34 @@
-{ ... } @ args:
-
+{ username, ... } @ args:
 #############################################################
 #
 #  Harmonica - my MacBook Pro 2020 13-inch, mainly for business.
 #
 #############################################################
-
 let
-  name = "harmonica";
-in
-{
+  hostname = "harmonica";
+in {
   imports = [
-    ../../modules/darwin/core.nix
-    ../../modules/darwin/apps.nix
+    ../../modules/darwin
 
     ../../secrets/darwin.nix
   ];
 
   nixpkgs.overlays = import ../../overlays args;
 
-  networking.hostName = name;
-  networking.computerName = name;
-  system.defaults.smb.NetBIOSName = name;
+  networking.hostName = hostname;
+  networking.computerName = hostname;
+  system.defaults.smb.NetBIOSName = hostname;
+
+  # Define a user account. Don't forget to set a password with ‘passwd’.
+  users.users."${username}" = {
+    home = "/Users/${username}";
+    description = username;
+
+    # set user's default shell back to zsh
+    #    `chsh -s /bin/zsh`
+    # DO NOT change the system's default shell to nushell! it will break some apps!
+    # It's better to change only starship/alacritty/vscode's shell to nushell!
+  };
+
+  nix.settings.trusted-users = [username];
 }