Address all code review issues

- XSS: use hx-confirm instead of onclick confirm()
- Feed: per-artist type filtering in SQL with LIMIT/OFFSET
- Cache: batch staleness check (single query)
- Monitoring: null-guard + constant-first equals
- REST stack: switch to reactive (quarkus-rest)
- User-Agent: fix double https, update version
- Settings: validate cache TTL before saving
- Delete: transactional cascade
- Docker: remove unused sqlite package
- Explicit columns in findAllArtists

src/main/resources/templates/fragments/artist-list.html

@@ -77,7 +77,7 @@
                   hx-delete="/api/artists/{artist.mbid}"
                   hx-target="#artist-list"
                   hx-swap="innerHTML"
-                  onclick="return confirm('Remove {artist.name}?')">
+                  hx-confirm="Remove {artist.name}?">
             <svg class="icon-sm" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><polyline points="3 6 5 6 21 6"/><path d="M19 6v14a2 2 0 01-2 2H7a2 2 0 01-2-2V6m3 0V4a2 2 0 012-2h4a2 2 0 012 2v2"/></svg>
           </button>
         </td>