add features.applications.shellScripts option

uses a custom function from my helper flake to convert a basic attrset of strings into a format `home.file` will accept

modules/features/shells/zsh.nix

@@ -7,8 +7,6 @@
 
     config = lib.mkIf (config.features.shells.zsh.enable) {
       programs.zsh.enable = true;
-      users.defaultUserShell = pkgs.zsh;
-      users.users."grey".shell = pkgs.zsh;
 
       home-manager.users.grey = lib.mkIf (config.features.nixos.home-manager.enable) {
         features.shells.zsh.enable = lib.mkDefault true;