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/delete_library.md

@@ -1,3 +1,11 @@
+---
+method: DELETE
+path: /api/libraries/:id
+auth: jwt+admin
+area: libraries
+---
+<!-- source: internal/handlers/library.go:152 LibraryHandler.DeleteLibrary -->
+
 # Delete Library
 
 Delete a library and all associated data.