Improve show record interface

Use a single column layout on mobile, with centered buttons.

lib/music_library_web/components/core_components.ex

@@ -427,7 +427,10 @@ defmodule MusicLibraryWeb.CoreComponents do
 
   def header(assigns) do
     ~H"""
-    <header class={[@actions != [] && "flex items-center justify-between gap-6 mb-2", @class]}>
+    <header class={[
+      @actions != [] && "sm:flex sm:items-center sm:justify-between sm:gap-6 mb-2",
+      @class
+    ]}>
       <div>
         <h1 class="text-lg font-semibold leading-8 text-zinc-800">
           <%= render_slot(@inner_block) %>
@@ -436,7 +439,7 @@ defmodule MusicLibraryWeb.CoreComponents do
           <%= render_slot(@subtitle) %>
         </p>
       </div>
-      <div class="flex-none"><%= render_slot(@actions) %></div>
+      <div class="flex justify-center gap-2 sm:flex-none mt-2 mb-2"><%= render_slot(@actions) %></div>
     </header>
     """
   end