docs(book-matching,collections): Beam batch 10 — 15 endpoints

WO3 sync internals resolved: the book-matching docs ARE the sync surface
(books/query, link-book, bulk/auto-link, unlinked-books, suggestions,
file-alias CRUD) + collections rule/test/bulk-assign/shelf-mapping
surface.

Dedupe resolved (Claude call): search_books.md declared
GET /api/books/match but its BODY documents POST /api/sync/books/query —
both routes exist and are distinct (query-param device protocol vs JSON
body plugin protocol). Repointed search_books.md frontmatter to the POST
route; get_book_matches.md keeps the GET.

Claude registry: 15 entries (one pre-existing link-book entry deduped).
Drift fixed by gate: auto-link request {confidence_threshold, limit} not
{device_id, threshold}; bulk-link link objects {unlinked_book_id,
media_item_id, confidence_score} not {device_id, book_id, ...};
responses {results,total,successful,failed}/{auto_linked,results}; added
missing example-responses (bare delete, remove-rule is_smart-after
semantics, bulk-assign per-book results). make test 9/9.

docs/developer/api/book-matching/get_unlinked_books.md

@@ -1,3 +1,11 @@
+---
+method: GET
+path: /api/devices/:deviceId/sync/unlinked-books
+auth: jwt
+area: book-matching
+---
+<!-- source: internal/handlers/matching.go:96 MatchingHandler.GetUnlinkedBooks -->
+
 # Get Unlinked Books
 
 Get all books that haven't been linked to media items yet for a specific device.
@@ -33,20 +41,10 @@ Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
 
 ## Response (200 OK)
 
-```json
+```json example-response
 {
-  "items": [
-    {
-      "id": "uuid",
-      "file_name": "book.epub",
-      "file_path": "/path/to/book.epub",
-      "size_bytes": 1234567,
-      "modified_at": "2026-02-08T10:00:00Z"
-    }
-  ],
   "total": 15,
-  "limit": 10,
-  "offset": 0
+  "unlinked": null
 }
 ```