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

Dockerfile

@@ -11,7 +11,6 @@ RUN mvn package -q -DskipTests
 # ─── 2. Runtime ───────────────────────────────────
 FROM eclipse-temurin:21-jre-alpine
 WORKDIR /app
-RUN apk add --no-cache sqlite
 COPY --from=build /build/target/quarkus-app/ /app/
 EXPOSE 8080