fix: 富友订单支持退款，0 元退款不强制客户收款材料映射

- decideRefundMethods 将 fuiou 与 wechat、alipay 按线上支付处理，修复富友订单报"该订单的支付方式不支持退款"
- 客户收款信息退款仅在金额大于 0 时强制映射并提交客户收款信息与凭证；0 元退款允许客户收款信息为空

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/application/wecom/scene.go

@@ -6,6 +6,7 @@ import (
 	"encoding/hex"
 	stdErrors "errors"
 	"fmt"
+	"strconv"
 	"strings"
 	"time"
 
@@ -332,6 +333,7 @@ func RequiredSceneFields(businessType string) []RequiredSceneField {
 }
 
 // RequiredRefundFields 返回退款提交固定与条件必需字段；快照方式编码缺失或未知时由表单构建拒绝。
+// 客户收款信息退款要求客户收款信息与凭证必须映射并提交；0 元退款不退钱，两者不强制。
 func RequiredRefundFields(snapshot map[string]any) []RequiredSceneField {
 	methodCode, ok := snapshot[constants.ApprovalFieldRefundMethodCode].(string)
 	methodCode = strings.TrimSpace(methodCode)
@@ -339,12 +341,22 @@ func RequiredRefundFields(snapshot map[string]any) []RequiredSceneField {
 		return []RequiredSceneField{{Code: constants.ApprovalFieldRefundMethodCode, Name: "退款方式编码"}}
 	}
 	result := []RequiredSceneField{{Code: constants.ApprovalFieldRefundMethod, Name: "退款方式", RequiredMapping: true}}
-	if methodCode == constants.RefundMethodCustomerAccount {
+	if methodCode == constants.RefundMethodCustomerAccount && !isZeroAmountRefund(snapshot) {
 		result = append(result, RequiredSceneField{Code: constants.ApprovalFieldCustomerAccountInfo, Name: "客户收款信息"}, RequiredSceneField{Code: constants.ApprovalFieldCustomerVoucherKey, Name: "客户收款凭证"})
 	}
 	return result
 }
 
+// isZeroAmountRefund 判断快照中的申请退款金额是否为 0；金额缺失或无法解析时按非 0 处理，保持强制校验。
+func isZeroAmountRefund(snapshot map[string]any) bool {
+	raw, ok := snapshot[constants.ApprovalFieldRequestedRefundAmount].(string)
+	if !ok {
+		return false
+	}
+	amount, err := strconv.ParseFloat(strings.TrimSpace(raw), 64)
+	return err == nil && amount == 0
+}
+
 // approvalBusinessTypes 返回全部已登记审批业务场景，供只读字段汇总复用。
 func approvalBusinessTypes() []string {
 	return []string{