Remove `unoptimized` flag from all thumbnail/cover Image components
and add proper responsive `sizes` props. Convert raw `<img>` tags on
the libraries page to next/image. Add 24h minimumCacheTTL for
optimized images. BookPreview keeps `unoptimized` since the API
already returns optimized WebP.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Add a new GET /authors endpoint that aggregates unique authors from books
with book/series counts, pagination and search. Add author filter to
GET /books. Backoffice gets a list page with search/sort and a detail
page showing the author's series and books.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
