Book: Example entry

This is an example library entry. Delete it once you have real entries.

extra.thumbnail is a path served from media/ (gitignored — see CLAUDE.md), not committed to the repo: drop an image at media/library/example-entry/thumbnail.jpg on the VPS and set thumbnail to /media/library/example-entry/thumbnail.jpg as above. Leave it unset (as here) and the entry just renders without one — no placeholder box. To pull one automatically from the link above instead of adding it by hand, run:

uv run scripts/fetch-thumbnail.py content/library/example-entry

(A bare filename like cover.jpg also works and is resolved as a colocated page-bundle image next to this index.md instead — fine for a one-off, but committed to git, unlike media/.)

extra.type becomes the "Book:", "Article:", "Video:", "Movie:" (etc.) prefix on the title. description doubles as the author/creator, shown in the meta line. Everything below the front matter is your own notes and comments about it, as normal Markdown.