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.

apps/site/src/content.config.ts

@@ -58,7 +58,7 @@ const bookshelf = defineCollection({
     url: z.string().optional(),
     cover_image: z.string().optional(),
     rating: z.number().optional(),
-    status: z.enum(["reading", "read", "abandoned"]).optional(),
+    read_status: z.enum(["reading", "read", "abandoned"]).optional(),
     date_started: z.coerce.date().optional(),
     date_finished: z.coerce.date().optional(),
     taxonomies,

apps/site/src/pages/bookshelf/index.astro

@@ -19,7 +19,7 @@ const items = (await getCollection("bookshelf")).sort(
         </h3>
         <p class="meta">{entry.data.authors.join(", ")}</p>
         {entry.data.rating && <p class="meta">{"★".repeat(entry.data.rating)}</p>}
-        {entry.data.status && <p class="meta">{entry.data.status}</p>}
+        {entry.data.read_status && <p class="meta">{entry.data.read_status}</p>}
         {entry.data.kind === "book" && entry.data.isbn && <p class="meta">ISBN {entry.data.isbn}</p>}
         {entry.data.kind === "paper" && entry.data.arxiv_id && (
           <p class="meta">