feat(loyalty): one-time EnakPoint payment code

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>

internal/handler/customer_pin_handler.go

@@ -136,3 +136,16 @@ func customerIDFromGin(c *gin.Context, method string) (uuid.UUID, bool) {
 func pinRequestInfo(c *gin.Context) models.CustomerPinRequestInfo {
 	return models.CustomerPinRequestInfo{IPAddress: c.ClientIP(), UserAgent: c.Request.UserAgent()}
 }
+
+// IssuePaymentCode is POST /customer/wallet/payment-code.
+func (h *CustomerPinHandler) IssuePaymentCode(c *gin.Context) {
+	customerID, ok := customerIDFromGin(c, "CustomerPinHandler::IssuePaymentCode")
+	if !ok {
+		return
+	}
+	var req contract.IssuePaymentCodeRequest
+	if !bindPinRequest(c, &req, "CustomerPinHandler::IssuePaymentCode") {
+		return
+	}
+	util.HandleResponse(c.Writer, c.Request, h.pinService.IssuePaymentCode(c.Request.Context(), customerID, &req, pinRequestInfo(c)), "CustomerPinHandler::IssuePaymentCode")
+}