docs(admin): libraries page — the definition surface, with backlinks

Fifth admin page and the section's hub. Documents library creation
(name/description/type — type fixed at creation, verified in the edit
modal), the card's Force Rescan + Manage controls, and the full panel:
folders (add via Browse or manual path, shallow per-folder scan,
removal-unregisters-only semantics verified in DeleteLibraryFolder —
files and items untouched, archive lifecycle governs the rest; podcast
roots refuse hand scans), User Access visibility checkboxes (default-
allow, DB-enforced), the processing-issues link, and Delete Library's
exact destructive scope (records + reading data gone, files on disk
untouched). Ends with the at-a-glance scan table linking scanning.md.
Adds the Libraries backlinks to the processing-issues and archived
pages. Glossary gains Create Library, Manage, Edit Details, Delete
Library, View Archived, Purge Archived Now, Browse, User Access.

docs/developer/ui-controls.md

@@ -252,6 +252,38 @@ label: Delete
 where: Admin → Archived Items rows, and other admin destructive rows
 does: Permanently removes the item and its reading history — no archive, no undo. Every Delete is confirm-guarded and states the scope.
 
+label: Create Library
+where: Admin → Libraries → page header
+does: Opens the create-library modal (name, optional description, library type). Type is fixed at creation — it cannot be edited later.
+
+label: Manage
+where: Admin → Libraries → a library's card row
+does: Opens that library's panel: folders, user access, processing issues, edit/delete.
+
+label: Edit Details
+where: Admin → Libraries → a library's panel
+does: Edits the library's name and description. Library type is not editable.
+
+label: Delete Library
+where: Admin → Libraries → a library's panel
+does: Permanently deletes the library, its folder mappings, and all book records with reading progress, highlights, notes, bookmarks, and ratings. Files on disk are not touched.
+
+label: View Archived
+where: Admin → Libraries → the archived banner
+does: Opens the Archived Items page.
+
+label: Purge Archived Now
+where: Admin → Libraries → the archived banner
+does: Same permanent wipe as Purge All Archived on the Archived Items page, offered inline.
+
+label: Browse
+where: Admin → Libraries → a library's panel → folder form
+does: Opens the server-side folder browser: walk the filesystem, Select This Folder fills the path input.
+
+label: User Access
+where: Admin → Libraries → a library's panel → section heading
+does: Per-user visibility checkboxes — checked (default) shows the library to that user; unchecked hides it everywhere for them, enforced in the database.
+
 label: Resume rewind
 where: audio player → player settings; profile settings
 does: Rewinds playback a configured few seconds when you resume.