Cron jobs using `deliver: whatsapp` were silently dropped because the
resolver's home-channel env var dict in cron/scheduler.py listed every
messaging platform except whatsapp. _resolve_delivery_targets() returned
[] and no message was sent — but jobs.json marked the run successful and
no log line surfaced the failure.
The gateway adapter and the send_message tool path both honored
WHATSAPP_HOME_CHANNEL correctly; only the cron path missed.
Adds 'whatsapp' -> 'WHATSAPP_HOME_CHANNEL' to _HOME_TARGET_ENV_VARS.
Verified end-to-end with multiple cron pings landing in WhatsApp
self-chat after the fix.
Fixes#22997
d8c4460fe3