- Public event detail page renders description/series-description/content
as markdown via useMarkdown, with prose styles; agenda becomes an
unordered list with the same custom bullets.
- Events list API returns `isRegistered` per event (derived from the
requester's registrations, ignoring cancelled rows), and the list page
shows a "Registered" tag. Stops exposing the full registrations array
in the list response.
- Removes the seats/sold-out/limited capacity UI from list and detail
pages.
- EventTicketPurchase: minor template formatting (self-closing inputs,
prettier wrapping).
