flake: rework modules folder structure

modules/home/shells/fish.nix

@@ -0,0 +1,23 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+{
+  options.settings.shell.fish = {
+    enable = lib.mkEnableOption "enable fish shell";
+  };
+
+  config = lib.mkIf config.settings.shell.fish.enable {
+    programs.fish = {
+      enable = true;
+      plugins = [
+        {
+          name = "fish-you-should-use";
+          src = pkgs.fishPlugins.fish-you-should-use;
+        }
+      ];
+    };
+  };
+}