rest of the split migration

modules/shell/config/nixos.nix

@@ -0,0 +1,32 @@
+{
+  config,
+  inputs,
+  lib,
+  pkgs,
+  ...
+}:
+{
+  options.my.shell = {
+    type = lib.mkOption {
+      type = lib.types.enum [
+        "bash"
+        "zsh"
+      ];
+      default = "bash";
+      description = "The shell to use system-wide (bash or zsh)";
+    };
+    users = lib.mkOption {
+      type = inputs.self.lib.usersOptionType lib;
+      default = config.my.toggleUsers.shell;
+      description = "Users to configure shell for";
+    };
+  };
+  config = {
+    users.users = lib.mkMerge (
+      map (user: {
+        ${user}.shell = pkgs.${config.my.shell.type};
+      }) (inputs.self.lib.normalizeUsers config.my.shell.users)
+    );
+    programs.zsh.enable = config.my.shell.type == "zsh";
+  };
+}