Transactional email health

The email_deliveries counts by state, and whether this deployment can send at all. suppressed is NOT a failure: it is what every delivery looks like while email is off, and it is the record of what would have gone out. dead is the dead-letter count, and those rows keep the reason in last_error. sent_unconfirmed is a send the provider told us had already happened under the idempotency key of this delivery itself, so there is no message id to record; it counts as delivered. stale is a dead row an operator retired by hand rather than re-sending.