支持客服入口按业务场景分流到客服分组

联系客服支持 scene（general/mohong），按用户与场景复用会话；摸大红入口走摸大红分组选人。

backend/internal/modules/chat/participant.go

@@ -21,6 +21,7 @@ type conversationRow struct {
 	LatestHandoffStatus string
 	LatestRefundStatus  string
 	Type                string
+	SupportScene        string
 	Title               string
 	Status              string
 	Role                string
@@ -37,7 +38,7 @@ type conversationRow struct {
 
 func (r *Repository) conversationQuery(ctx context.Context, principal Principal) *gorm.DB {
 	return r.db.WithContext(ctx).Table("chat_conversations AS c").
-		Select(`c.id, c.order_id, c.listing_id, c.type, c.title, c.status, c.last_message_id,
+		Select(`c.id, c.order_id, c.listing_id, c.type, c.support_scene, c.title, c.status, c.last_message_id,
 			c.last_message_preview, c.last_message_at, c.created_at, c.updated_at, cp.role,
 			(
 				SELECT COUNT(1)
@@ -300,6 +301,7 @@ func (row conversationRow) toDTO(participants []ParticipantDTO) ConversationDTO
 		LatestHandoffStatus: row.LatestHandoffStatus,
 		LatestRefundStatus:  row.LatestRefundStatus,
 		Type:                row.Type,
+		SupportScene:        row.SupportScene,
 		Title:               row.Title,
 		Status:              row.Status,
 		Role:                row.Role,