chore(release): 版本发布 - 发布 v1.2.8.rc3 候选版本

修复生产前端 Rolldown 分包循环依赖白屏，补齐画布引用排序与素材 payload 合同，并同步工作流生成素材字段。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/service/user_data.go

@@ -65,7 +65,7 @@ func (s *Service) UserAsset(userID string, id string) (json.RawMessage, error) {
 	if err != nil {
 		return nil, err
 	}
-	return json.RawMessage(asset.PayloadJSON), nil
+	return clientAssetPayload(*asset), nil
 }
 
 func (s *Service) UpsertUserAsset(userID string, raw json.RawMessage) (UserDataSummary, error) {
@@ -129,8 +129,8 @@ func (s *Service) UserAssets(userID string) ([]json.RawMessage, error) {
 	}
 	result := make([]json.RawMessage, 0, len(assets))
 	for _, asset := range assets {
-		if strings.TrimSpace(asset.PayloadJSON) != "" {
-			result = append(result, json.RawMessage(asset.PayloadJSON))
+		if payload := clientAssetPayload(asset); len(payload) > 0 {
+			result = append(result, payload)
 		}
 	}
 	return result, nil