- Add 'calls' to the WhatsApp WABA override_callback subscribed_fields so a
fresh embedded-signup connection (or a re-register) automatically receives
call webhooks from Meta. Previously required a manual App Dashboard step.
- Gate Channel::Whatsapp#voice_enabled? on the account-level 'channel_voice'
feature flag, matching the entitlement Twilio voice channel creation
already requires. Cascades through the controller, webhook services, and
inbox jbuilder voice_enabled serialization (FE button hides automatically).