feat(退款): AUG26-006 补充当前退款套餐已用量与总量

补齐 PRD §2.3.1「退款管理补充字段」：退款列表、详情与导出新增
「当前退款套餐已用量」与「当前退款套餐总量」两个纯展示字段。

- 套餐定位口径与退款套餐失效保持一致，按优先级取唯一一条：
  冻结的 package_usage_id（且属于该订单）→ 订单主套餐 → 订单任一套餐，
  同级按标识升序。不按当前世代或当前生效套餐推断；不按套餐状态过滤，
  使退款后套餐转已失效时仍能回看用量。
- 列表与详情用固定两次查询批量解析（按标识、按订单），查询次数不随条数增长；
  详情复用同一函数。解析不到套餐或记录已物理删除时返回 0，不阻断读取。
- 导出新增两列并改用同一优先级的 LATERAL 取法，不再依赖只按 r.package_usage_id
  的 join——生产库 1296 条退款仅 157 条带该字段，旧取法会让多数行显示零值。
- 不改变退款金额校验、冻结实收、套餐失效、接续、停机与佣金回溯任何规则。

验证：测试库 junhong_cmp_test 实测冻结记录、订单主套餐回退、记录缺失返回 0 三项
解析场景与「4 条退款固定 2 次查询」；并以同批 43 条退款对拍 Go 解析器与导出 SQL，
口径不一致 0 条；导出 43 行列数与表头一致。无迁移、无接口路径变化。

internal/exporter/refund_scene.go

@@ -2,6 +2,7 @@ package exporter
 
 import (
 	"context"
+	"strconv"
 	"time"
 
 	"gorm.io/gorm"
@@ -38,7 +39,8 @@ func (s *RefundDataSource) Count(ctx context.Context, params ExportParams) (int,
 // Headers 返回退款记录导出表头。
 func (s *RefundDataSource) Headers(context.Context, ExportParams) ([]string, error) {
 	return []string{
-		"退款单号", "代理店铺名称", "关联的支付订单号", "资产类型", "资产标识", "套餐名称", "原订单金额(元)",
+		"退款单号", "代理店铺名称", "关联的支付订单号", "资产类型", "资产标识", "套餐名称",
+		"当前退款套餐已用量(MB)", "当前退款套餐总量(MB)", "原订单金额(元)",
 		"实收金额(元)", "可退金额(元)", "申请退款金额(元)", "实际退款金额(元)", "状态", "退款方式",
 		"冻结实收金额(元)", "渠道退款状态", "渠道退款流水号", "渠道退款金额(元)", "失败分类", "异常标记",
 		"退款原因", "审批备注",
@@ -80,6 +82,10 @@ func (s *RefundDataSource) Fetch(ctx context.Context, params ExportParams, offse
 			o.total_amount AS original_amount,
 			o.actual_paid_amount AS refundable_amount,
 			COALESCE(pu.package_name, items.package_names, '') AS package_name,
+			-- 当前退款套餐用量：与展示口径一致，按冻结套餐记录 → 订单主套餐 → 订单任一套餐
+			-- 取唯一一条，且不按套餐状态过滤（退款后套餐已失效仍需展示其用量）。
+			COALESCE(usage.data_usage_mb, 0) AS refund_package_used_mb,
+			COALESCE(usage.data_limit_mb, 0) AS refund_package_total_mb,
 			COALESCE(ac.username, '') AS submitter_name,
 			ai.provider AS approval_provider,
 			ai.status AS approval_status,
@@ -96,6 +102,21 @@ func (s *RefundDataSource) Fetch(ctx context.Context, params ExportParams, offse
 			FROM tb_order_item AS oi
 			WHERE oi.order_id = r.order_id AND oi.deleted_at IS NULL
 		) AS items ON TRUE`).
+		Joins(`LEFT JOIN LATERAL (
+			SELECT candidate.data_usage_mb, candidate.data_limit_mb
+			FROM tb_package_usage AS candidate
+			WHERE candidate.deleted_at IS NULL
+			  AND (
+			    (r.package_usage_id IS NOT NULL AND candidate.id = r.package_usage_id AND candidate.order_id = r.order_id)
+			    OR (candidate.order_id = r.order_id)
+			  )
+			ORDER BY
+			  CASE WHEN r.package_usage_id IS NOT NULL AND candidate.id = r.package_usage_id THEN 0
+			       WHEN candidate.master_usage_id IS NULL THEN 1
+			       ELSE 2 END,
+			  candidate.id ASC
+			LIMIT 1
+		) AS usage ON TRUE`).
 		Order("r.id ASC").
 		Limit(limit).
 		Offset(offset)
@@ -112,6 +133,8 @@ func (s *RefundDataSource) Fetch(ctx context.Context, params ExportParams, offse
 			formatRefundAssetType(item.OrderType),
 			item.AssetIdentifier,
 			item.PackageName,
+			strconv.FormatInt(item.RefundPackageUsedMB, 10),
+			strconv.FormatInt(item.RefundPackageTotalMB, 10),
 			formatOptionalMoneyYuan(item.OriginalAmount),
 			formatMoneyYuan(item.ActualReceivedAmount),
 			formatOptionalMoneyYuan(item.RefundableAmount),
@@ -167,6 +190,8 @@ type refundExportRow struct {
 	OrderType                  string     `gorm:"column:order_type"`
 	AssetIdentifier            string     `gorm:"column:asset_identifier"`
 	PackageName                string     `gorm:"column:package_name"`
+	RefundPackageUsedMB        int64      `gorm:"column:refund_package_used_mb"`
+	RefundPackageTotalMB       int64      `gorm:"column:refund_package_total_mb"`
 	OriginalAmount             *int64     `gorm:"column:original_amount"`
 	ActualReceivedAmount       int64      `gorm:"column:actual_received_amount"`
 	RefundableAmount           *int64     `gorm:"column:refundable_amount"`