Get people in without selling

1. Invite: the host enters an email and a ticket type. The person gets an email and an unclaimed ticket. One invite or walk-in per person; the email can be sent again until they sign in.
2. Import: the host uploads a CSV of tickets sold on Luma or Eventbrite, with the columns external_ticket_id, email, platform, ticket_type, and optionally name, organization, title. The ticket types must exist. One bad row rejects the file, with every problem listed; uploading twice skips what is already in. Each ticket keeps its barcode so the desk can scan it. No email goes out; the person gets one at their first check-in.
3. A host's own registration form adds attendees with an API key, one at a time, as rows of the same shape: each names a platform and an external ticket id.
4. Walk-in: if the event allows it, staff issue a ticket at the door, already claimed.

Rules: imports do not check the free cap, and a full event is charged the blocks an import crosses.