GET /auth/bifrost/register renders the form (notice in full, unchecked consent box);
POST /auth/bifrost/register/form and the JSON endpoint share NativeRegistration.
Challenge payload gains issued-at; waited path needs FallbackWaitSeconds and a
stricter per-address FallbackPermits budget.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>