feat(nix): migrate Neovim to Nix (as a symlink)

nix/home/neovim/nvim/lua/plugins/highlight-undo.lua

@@ -0,0 +1,15 @@
+-- highlight-undo.nvim
+-- https://github.com/tzachar/highlight-undo.nvim
+return {
+  "tzachar/highlight-undo.nvim",
+  config = function()
+    require("highlight-undo").setup({
+      hlgroup = "HighlightUndo",
+      duration = 300,
+      keymaps = {
+        { "n", "u", "undo", {} },
+        { "n", "<C-r>", "redo", {} },
+      },
+    })
+  end,
+}