feat: nixvim refactor

modules/home-manager/programs/nixvim/presets/undotree.nix

@@ -0,0 +1,22 @@
+{ lib, config, ... }:
+let
+  cfg = config.presets.undotree;
+in
+{
+  options.presets.undotree = {
+    enable = lib.mkEnableOption "Undotree";
+  };
+
+  config = lib.mkIf cfg.enable {
+    opts = {
+      undodir = {
+        __raw = "os.getenv('HOME') .. '/.config/nvim/undodir'";
+      };
+      undofile = true;
+    };
+    plugins = {
+      undotree.enable = true;
+      which-key.registrations."<leader>u" = "Undotree";
+    };
+  };
+}