better consistency, add dotfiles for takamaki and new features

modules/features/shells.nix

@@ -1,9 +1,7 @@
 { inputs, self, ... }: {
   flake.nixosModules.global = { config, pkgs, lib, ... }: {
     options.features.shells.defaultShell = lib.mkOption {
-      type = lib.types.enum (map (name: lib.removeSuffix ".nix" name) (
-        builtins.attrNames (builtins.readDir "${self}/modules/features/shells")
-      ));
+      type = inputs.helpers.mkEnumFromDirContents "${self}/modules/features/shells";
       default = "zsh";
     };