fix(visitor_mailer): don't re-invite visitors when an event changes room (PPT-2375)

[chillfox]

Scenario 5 of PPT-2375: "Email notification to all visitors if the location changes — this is working, but the additional email trigger visitor_invited.event should be stopped."

Why it happens

Moving an event to another room makes the staff API re-announce every visitor already attending it on staff/guest/attending, identically to a genuine new invitation. The driver turned each one into a full invitation email on top of the change notification, so visitors got both.

The payloads are indistinguishable, so the driver correlates the two signals instead: an invite arriving as meeting_update is held for the debounce window and dropped if a change notification for the same event turns up. Matched on event_ical_uid and event_id, because either can be missing, and the staff API spawns both signals concurrently so neither order is guaranteed. A short memory of recently changed events covers an invite that arrives after the change email has already gone out, which is also what makes it work with event_change_debounce: 0.

Brand new invitations (meeting_created) are never held.

Also here

The change notification now carries guest_jwt, kiosk_url and the same inline qr.png as an invitation — a move invalidates the kiosk link issued with the original invite (its token is scoped to the old room) and the invite is no longer re-sent. The templates need updating to reference them, or disable_qr_code: true to leave the attachment off.

Trade-offs

• invitations for visitors added to an existing event are delayed by the debounce window,
• a visitor added by the same edit that moved the room gets the change notification instead of an invitation — they are in the event guest list, so they are still emailed, and they now get a QR code and kiosk link with it.

Testing

14 new specs: both signal orders, several visitors, invites that must still be sent, meeting_created, event_change_debounce: 0, suppression scoped per event, matching by event_id alone, draining held invites, and the QR/kiosk fields on both changed templates.

./harness report --basic-render --verbose --tests=1 drivers/place/visitor_mailer_spec.cr passes; crystal tool format and ameba clean.

Paired with PlaceOS/staff-api#382, which stops the re-announcement at source. This PR does not depend on it.