Introduce typed token value objects (EventToken, OrganizerToken,
RsvpToken) and refactor all existing Event code to use them.
Add POST /events/{token}/rsvps endpoint that persists an RSVP and
returns an rsvpToken. Populate attendeeCount in GET /events/{token}
from a real count query instead of hardcoded 0.
Includes: OpenAPI spec, Liquibase migration (rsvps table with
ON DELETE CASCADE), domain model, hexagonal ports/adapters,
service layer, and full test coverage (unit + integration).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
