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/support.go

@@ -213,7 +213,7 @@ func (r *Repository) listAdminConversations(ctx context.Context, principal Princ
 	var rows []conversationRow
 	offset := (page - 1) * pageSize
 	queryDB := r.adminConversationBase(ctx, principal, keyword).
-		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,
 			COALESCE(cp_me.role, 'admin') AS role,
 			lo.id AS latest_order_id, lo.order_no AS latest_order_no, lo.status AS latest_order_status,