Start Checkout

Create a Stripe Checkout session and return its hosted URL.

Requires the paid-order legal data the upgrade form already collects (account_type + country, §§ 13/14 BGB and the VAT jurisdiction). It does not re-collect them: rejecting with a pointer at the existing form keeps ONE place where that data is captured, which is also where backend#145 will attach the § 312j/§ 356 V surface.