Detect unsent/deleted Airbnb messages via Public API and Webhooks

Currently, when a guest unsends or deletes a message on Airbnb, this state is reflected in the Hospitable inbox (with a bin icon and deletion timestamp), but it is not exposed via the Public API or webhooks.

The request is to provide a way to detect these deletions—either through a deletion flag/timestamp in the message object, a dedicated endpoint, or a webhook notification. This would allow developers to flag unsent messages in their own systems and warn users who may be replying to a message that the guest has already retracted.