Trigger Deliverability Report

Build the daily deliverability snapshot (recipient-ESP + ESP-match cuts, each for a 7d and a 24h window) and post it to #notifications.

The recipient-ESP resolution is heavy (~3 min over ~400k sends) so it runs in a worker thread, off the event loop; the cron curls with a long -m and the CronJob's activeDeadlineSeconds bounds the pod. Best-effort — never raises into the cron.