After Synapse's systemd health check passes, Traefik still needs
providers.providersThrottleDuration to register routes. Derive the
post-start delay from this setting (+1s for healthcheck polling gap)
instead of using a hardcoded value. Defaults to 0 when no Traefik
reverse proxy is used.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>