For true privacy don't use SMS/Phone number for notification

SMS systems can be hacked/monitored. Suggest instead of using SMS that an encrypted push notification be utilized between devices for notification.

Start by mapping Haven's current SMS and phone-number notification flow in the Android app. Then investigate the requirements and trade-offs for encrypted push notifications between devices. Done would require a defined replacement path that preserves notification delivery without relying on SMS or phone numbers.

Written by the indexing model from the issue text.