Fix UI inconsistencies across templates

- Replace .separator with .dropdown_separator in 4 dropdown menus
- Change gray-* to zinc-* color classes in online store templates
- Wrap hardcoded page titles in gettext() in online store templates
- Add consistent dark:text-zinc-200 to maintenance h3 subsections
- Add text-zinc-900 dark:text-zinc-200 to scrobble section headers
- Fix heading hierarchy (h1/h2 → h2/h3) in record set items
- Align artist form modal header to text-lg font-semibold
- Use size="xs" prop instead of class override on format badge
- Add external link icon to wishlist online store buttons

lib/music_library_web/components/record_components.ex

@@ -407,7 +407,7 @@ defmodule MusicLibraryWeb.RecordComponents do
 
   defp format_badge(assigns) do
     ~H"""
-    <.badge class="text-xs md:text-sm">
+    <.badge size="xs">
       {@release |> ReleaseSearchResult.format() |> format_label()}
     </.badge>
     """