The POST /modules/stripe/invoice endpoint was retired in PR #327 (always
returns HTTP 410 with code stripe_email_payment_disabled). This patch
aligns the public OpenAPI spec with the new behaviour, documents the
legacy DELETE /modules/stripe/invoice cleanup route, and adds a unit
test that guards the documentation so future contributors cannot
silently un-retire the payment-link creation route.
Refs: TRU-74 / DRIFT 13