feat: add Airwallex payments and multi-currency support

backend/internal/payment/provider/factory.go

@@ -17,6 +17,8 @@ func CreateProvider(providerKey string, instanceID string, config map[string]str
 		return NewWxpay(instanceID, config)
 	case payment.TypeStripe:
 		return NewStripe(instanceID, config)
+	case payment.TypeAirwallex:
+		return NewAirwallex(instanceID, config)
 	default:
 		return nil, fmt.Errorf("unknown provider key: %s", providerKey)
 	}