convey: localhost-only bind by default + opt-in network access
Flip fresh installs to bind localhost-only unless convey.allow_network_access is explicitly enabled, and default localhost requests to trusted unless configured otherwise. Seed the new convey defaults in journal config and write them during init finalization so new installs and fixture journals agree.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>