Fix search dropdown, async artist add, OOB swaps

- Fix search results dropdown: absolute position relative to search wrapper
- Make release group fetching async via Vert.x executeBlocking (avoid blocking add)
- Add OOB swap for artist list so +Add works from any page
- Simplify search-results template styling
- Add Response type for combined OOB responses

src/main/resources/templates/fragments/search-results.html

@@ -1,4 +1,4 @@
-<div class="card bg-base-100 shadow-xl mt-1 max-h-64 overflow-y-auto">
+<div class="bg-base-100 shadow-xl border border-base-300 rounded-box mt-1 max-h-64 overflow-y-auto">
   {#if artists.isEmpty()}
     <div class="p-3 text-sm text-base-content/60">No artists found</div>
   {#else}
@@ -18,9 +18,9 @@
         {#else}
           <button class="btn btn-primary btn-xs"
                   hx-post="/api/artists/{artist.mbid}/track"
-                  hx-target="#artist-list"
+                  hx-target="#search-results"
                   hx-swap="innerHTML"
-                  onclick="this.closest('#search-results').innerHTML=''; document.querySelector('[name=q]').value=''">
+                  onclick="document.getElementById('search-input').value=''">
             + Add
           </button>
         {/if}