Adds POST /customer/wallet/payment-code (docs/prd-point-coin.md F9, K8,
PC-304). The customer approves with their PIN on their own phone and gets a
6-digit code, as digits and as a QR payload (enakpoint:<code>) for the app
to render, valid for two minutes. The PIN is never typed at the cashier.
Codes are drawn from crypto/rand and stored in Redis with SET NX and a TTL,
bound to the customer; a new code retires the previous one. Redeeming is a
single Lua step that uses the code up only if it belongs to the order's
customer, so it stays one-time under a race, and a cashier scanning it
against the wrong order does not burn it for its owner, which a plain
GETDEL would. Expired, used, unknown and other customers' codes are all
refused alike.
Tests run against miniredis, added as a test dependency.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
