Get the newest attendees across all listings without decrypting PII. Used for the admin dashboard to show recent registrations.

The limit counts ATTENDEES, not booking lines: the inner subquery picks the newest limit attendee ids — by id, which is AUTOINCREMENT and so co-monotonic with created but index-backed (no sort over the whole unbounded attendees table) — and the outer LEFT JOIN returns every booking line for those attendees, so the dashboard's grouped rows always carry an attendee's complete listings.