Restructure Darwin configuration

So far, this is just based on mightymac. The other devices will be
updated soon.

modules/hosts/common/files/nvim/lua/plugins/todo-comments.lua

@@ -0,0 +1,9 @@
+return {
+	"folke/todo-comments.nvim",
+	dependencies = { "nvim-lua/plenary.nvim" },
+	opts = {
+		-- your configuration comes here
+		-- or leave it empty to use the default settings
+		-- refer to the configuration section below
+	},
+}