Add bookshelf ISBN/paper enrichment, fix status field name collision

apps/cms/src/utils/bookshelf-covers.ts fetches book covers from Open
Library by ISBN (real image, cached into apps/site/public/covers/)
and backfills missing title/authors for papers from Semantic Scholar
by DOI/arXiv id. Wired into the sync middleware in content-sync.ts:
runs once per entry (cover_image already set means "done"), and only
on live create/update through Strapi, not during the boot-time
import (so a restart doesn't hammer external APIs).

Also renames the bookshelf `status` field to `read_status`
everywhere (schema, content/README.md, seed content, Astro zod
schema, bookshelf page, sync mapping). Strapi's content-manager API
treats a top-level `status` key as its own reserved draft/publish
parameter even with draftAndPublish disabled, so an attribute
literally named `status` silently rejected every write — caught this
while testing the enrichment hook.

Verified end-to-end: created a book by ISBN with no cover_image,
confirmed a real cover image was downloaded and cached, cover_image
was set on the entry and written to the file, and the cover/file were
both removed on delete.

content/bookshelf/attention-is-all-you-need.md

@@ -7,7 +7,7 @@ arxiv_id = "1706.03762"
 url = "https://arxiv.org/abs/1706.03762"
 cover_image = "/covers/attention-is-all-you-need.jpg"
 rating = 5
-status = "read"
+read_status = "read"
 date_started = 2026-02-01
 date_finished = 2026-02-03
 [taxonomies]

content/bookshelf/structure-and-interpretation-of-computer-programs.md

@@ -5,7 +5,7 @@ authors = ["Harold Abelson", "Gerald Jay Sussman"]
 isbn = "9780262510875"
 cover_image = "/covers/structure-and-interpretation-of-computer-programs.jpg"
 rating = 5
-status = "read"
+read_status = "read"
 date_started = 2026-01-01
 date_finished = 2026-01-20
 [taxonomies]