docs(libraries): Beam WO5 batch 5 — 11 endpoints backfilled + pilot recovery

Beam backfilled 11 library docs (CRUD, folders, visibility, browse, stats,
media-items) and re-attached frontmatter to create_collection.md — which had
silently lost its pilot version in cc893f75: the negative-test
'git checkout --' restored the OLD file because the pilot was never staged,
and a frontmatter-less doc is invisible to the gate. Claude restored the full
corrected pilot content (priority higher-wins, time.String() note, 409).

Claude registry: 11 entries + one inverted catch — DELETE /:id/folders DOES
bind {folder_path} (handler reuses AddLibraryFolderRequest); registry first
draft said bodyless. GET /:id/visibility returns joined
GetUserVisibleLibrariesRow (type_name etc.), not bare Libraries.

Gate-driven merges fixed create/get library response shapes (sqlc row keys:
created_by_admin_id, library_type_id, updated_at; dropped invented type/
folders/is_visible). Fixed invented request fields (user_id in
set-visibility; library_type_id in update). make test 9/9.

docs/developer/api/libraries/get_library_stats.md

@@ -1,3 +1,11 @@
+---
+method: GET
+path: /api/libraries/:id/stats
+auth: jwt+admin
+area: libraries
+---
+<!-- source: internal/handlers/library.go:303 LibraryHandler.GetLibraryStats -->
+
 # Get Library Statistics
 
 Get statistics for a specific library.
@@ -26,18 +34,14 @@ Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
 
 ## Response (200 OK)
 
-```json
+```json example-response
 {
   "library_id": "uuid",
-  "total_media_items": 1523,
-  "total_size_bytes": 5368709120,
-  "last_scan": "2026-02-08T10:00:00Z",
-  "formats": {
-    "epub": 1234,
-    "kepub": 189,
-    "mobi": 50,
-    "pdf": 50
-  }
+  "books": null,
+  "minutes": null,
+  "name": null,
+  "pages": null,
+  "sessions": null
 }
 ```