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/admin/archived-items.md

@@ -16,8 +16,8 @@ then — or after — the reader's history is preserved, so a file that comes
 back (or a move the scanner detects automatically) restores the item with
 its reading data intact.
 
-You reach this page from the Libraries page, which shows an **Archived
-items** banner with the count whenever anything is archived.
+You reach this page from the [Libraries](libraries.md) page, which shows
+an **Archived items** banner with the count whenever anything is archived.
 
 ## What the page shows