Fourth admin page. Documents the two-consecutive-scans archive rule,
the history-preserving rationale, ARCHIVE_RETENTION_DAYS (default 90,
0 = manual-purge-only, verified in config.go), and the four actions with
verified semantics: Merge (progress/annotations/collections folded into
the active copy, per-user collisions keep the active copy — mirrors
hash-conflict resolution), Restore (immediate; re-archives if the file
is truly still gone), Delete (item + history, permanent), Purge All
Archived (the clean-slate button, confirm text quoted). Links to
scanning.md for why only library-wide scans archive. Glossary gains
Purge All Archived, Merge, and a scoped generic Delete entry.
