Redeem a voucher into the customer vault

Accepts a rewards voucher and books its value into the voucher vault for a customer who has no active MVNO account yet. The vault row drains automatically when the account becomes ACTIVE (DMA + RICA complete). Idempotent for retries: replaying the same voucher after a successful vault redemption returns the existing redemption (no double deposit). A voucher already redeemed directly to an account returns 400.

Access: Auth methods: JWT bearer or API key. Allowed user types: MVNO. Requires permissions: voucher:create.