Events can take a waitlist for sold-out lines. When places free up
(cancellation, smaller booking, higher stock limit) the next person is
offered them with a claim link and the places are held for a set time;
unclaimed offers expire and move on, with optional partial offers. Stock
is now counted in one place (utils/stock.js), including held places,
and manual registrations and booking edits are now stock-checked. Adds a
supervisor waitlist page, My Events waitlists, and the daily summary count.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
