Redeem a promotion code

Redeems one promotion code for the verified organization, with the billing owner's explicit confirmation. A code carries one benefit: promotional execution credit that expires and is spent before purchased credit, a complimentary slot for a named project that never becomes a paid subscription, a perk, or a discount on the project subscription shown in the next project quote. Every code that cannot be redeemed — unknown, ended, used up, not for this organization, or not combinable with a benefit already held — receives the same not_found answer; repeated refusals are throttled with rate_limited. The Idempotency-Key makes retries return the original grant. Nothing is charged and no payment method is needed.