Auto-generate the provisioning shared secret (to enable the provisioning
API), route the whole mautrix-whatsapp HTTP port via Traefik under
`<matrix-fqn>/bridges/whatsapp`, and populate appservice.public_address,
reusing the matrix_bridges_exposure_* mechanism.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>