feat: first take at UI app

lib/bds/desktop/menu.ex

@@ -0,0 +1,42 @@
+defmodule BDS.Desktop.Menu do
+  @moduledoc false
+
+  use Desktop.Menu
+  alias Desktop.Window
+
+  @impl true
+  def mount(menu) do
+    {:ok, menu}
+  end
+
+  @impl true
+  def render(assigns) do
+    ~H"""
+    <menu>
+      <item onclick="open">Open</item>
+      <hr />
+      <item onclick="quit">Quit</item>
+    </menu>
+    """
+  end
+
+  @impl true
+  def handle_event("open", menu) do
+    Window.show(BDS.Desktop.MainWindow)
+    {:noreply, menu}
+  end
+
+  def handle_event("quit", menu) do
+    Window.quit()
+    {:noreply, menu}
+  end
+
+  def handle_event(_, menu) do
+    {:noreply, menu}
+  end
+
+  @impl true
+  def handle_info(_, menu) do
+    {:noreply, menu}
+  end
+end