docs(media-items,collections,koreader,admin): Beam batch 11 — final backfill

All remaining endpoint docs frontmatter'd: media-item bulk ops + audio
surface, collections book-listing/preview, koreader rating/review/stats
plugin protocol, hash-conflicts JSON list.

Scope call (Claude): resolve_hash_conflict.md DELETED — the resolve POST
renders an htmx fragment (renderResolved), a web-admin flow under rule 3;
only the GET list is a JSON API. update_media_review skipped by Beam
(correct): ratings/upsert_media_review.md already covers the PUT.

Registry: 16 entries. koreader rating/review/stats all bind
koreaderBookRef (query or body) — odd=half-star rating scale; audio track
endpoint serves raw bytes (ServeContent, Range) — response nil. Fixed
drift: deleted_annotations doc's secondary restore/purge fences
unlabeled (gate validates labeled blocks against the ONE frontmatter
route); chapters example labeled. UNVERIFIED: 1 (koreader book-ref
fields, push_stats). make test 9/9.

docs/developer/api/media-items/get_audio_track.md

@@ -1,3 +1,11 @@
+---
+method: GET
+path: /api/media-items/:id/audio/:trackIndex
+auth: jwt
+area: media-items
+---
+<!-- source: internal/handlers/media.go:3088 MediaHandler.GetAudioTrack -->
+
 # Get Audio Track
 
 Streams one playable track of a multi-file audiobook (folder-of-tracks