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/live/scrobble_rules_live/index.ex

@@ -134,7 +134,7 @@ defmodule MusicLibraryWeb.ScrobbleRulesLive.Index do
                 >
                   {gettext("Edit")}
                 </.dropdown_link>
-                <.separator />
+                <.dropdown_separator />
                 <.dropdown_button
                   phx-click="delete"
                   phx-value-id={scrobble_rule.id}