fix(billing): 异步任务退款时同步减少 used_quota (#6795)

* fix(billing): 异步任务退款时同步减少 used_quota
退款时仅恢复了 quota（剩余额度），但未同步减少 used_quota（已用额度），
导致"总额度"（quota + used_quota）随退款次数持续虚增，超出用户实际充值金额。

修复三处退款路径：
- RefundTaskQuota：任务失败完整退款
- RecalculateTaskQuota：差额结算退款分支
- controller/midjourney.go：Midjourney 任务失败退款

新增 model.UpdateUserUsedQuota 公开函数，仅调整 used_quota 不影响 request_count。

* fix(billing): 任务退款时同步扣减渠道 used_quota

* fix(billing): complete async task refund accounting

* style(model): group internal Midjourney fields

---------

Co-authored-by: CaIon <i@caion.me>

service/quota.go

@@ -406,17 +406,27 @@ func PreConsumeTokenQuota(relayInfo *relaycommon.RelayInfo, quota int) error {
 	return nil
 }
 
-func PostConsumeQuota(relayInfo *relaycommon.RelayInfo, quota int, preConsumedQuota int, sendEmail bool) (err error) {
+type postConsumeQuotaResult struct {
+	FundingApplied bool
+	TokenApplied   bool
+}
+
+func PostConsumeQuota(relayInfo *relaycommon.RelayInfo, quota int, preConsumedQuota int, sendEmail bool) error {
+	_, err := postConsumeQuotaWithResult(relayInfo, quota, preConsumedQuota, sendEmail)
+	return err
+}
+
+func postConsumeQuotaWithResult(relayInfo *relaycommon.RelayInfo, quota int, preConsumedQuota int, sendEmail bool) (result postConsumeQuotaResult, err error) {
 
 	// 1) Consume from wallet quota OR subscription item
 	if relayInfo != nil && relayInfo.BillingSource == BillingSourceSubscription {
 		if relayInfo.SubscriptionId == 0 {
-			return errors.New("subscription id is missing")
+			return result, errors.New("subscription id is missing")
 		}
 		delta := int64(quota)
 		if delta != 0 {
 			if err := model.PostConsumeUserSubscriptionDelta(relayInfo.SubscriptionId, delta); err != nil {
-				return err
+				return result, err
 			}
 			relayInfo.SubscriptionPostDelta += delta
 		}
@@ -428,9 +438,10 @@ func PostConsumeQuota(relayInfo *relaycommon.RelayInfo, quota int, preConsumedQu
 			err = model.IncreaseUserQuota(relayInfo.UserId, -quota, false)
 		}
 		if err != nil {
-			return err
+			return result, err
 		}
 	}
+	result.FundingApplied = true
 
 	if !relayInfo.IsPlayground {
 		if quota > 0 {
@@ -439,8 +450,9 @@ func PostConsumeQuota(relayInfo *relaycommon.RelayInfo, quota int, preConsumedQu
 			err = model.IncreaseTokenQuota(relayInfo.TokenId, relayInfo.TokenKey, -quota)
 		}
 		if err != nil {
-			return err
+			return result, err
 		}
+		result.TokenApplied = true
 	}
 
 	if sendEmail {
@@ -449,7 +461,7 @@ func PostConsumeQuota(relayInfo *relaycommon.RelayInfo, quota int, preConsumedQu
 		}
 	}
 
-	return nil
+	return result, nil
 }
 
 func checkAndSendQuotaNotify(relayInfo *relaycommon.RelayInfo, quota int, preConsumedQuota int) {