When a book is not in the local DB and the preview endpoint is hit,
metadata and the chapter index are now saved to PocketBase in the
background. Subsequent visits load from the local store instead of
scraping live. Chapter text is not fetched until an explicit scrape job
is triggered.
Adds GET /api/book-preview/{slug} and GET /api/chapter-text-preview/{slug}/{n}
Go endpoints that scrape live from novelfire.net without persisting to
PocketBase or MinIO. The UI book page falls back to the preview endpoint when
a book is not found in PocketBase, showing a 'not in library' badge and the
scraped chapter list. Chapter pages handle ?preview=1 to fetch and render
chapter text live, skipping MinIO and suppressing the audio player.