Hi.Events 1.9.0 - Unauthenticated Attendee PII Exposure via Check-in List short_id

Hi.Events through 1.9.0 public check-in list endpoints use short_id as sole access control, allowing unauthenticated access to retrieve full attendee lists including emails and personal information. Attackers with knowledge of the short_id can call GET /api/public/check-in-lists/{short_id}/attendees to read attendee data and create or delete check-in records without authentication.