Registration put every new customer into a hardcoded organization id,
which does not exist in staging, so set-password failed on the
fk_customers_organization foreign key with a 500.
POST /customer-auth/register/start now takes organization_id, the
organization the app is built for. It must be a UUID of an existing
organization, checked before the OTP is sent; it is kept in the OTP
session and set-password creates the customer there. A registration
started before this change has no organization in its session and is asked
to start again.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>