👑 [需求]导出图片，FlowEditor增加自动布局，自定义边缘，边缘增加样式，自适应画布方法

### 🥰 需求描述

1、导出流程图
2、FlowEditor加上自动布局，自适应画布方法，支持自定义边缘
3、边缘增加样式（颜色，粗细，箭头样式），设置节点间是否可以重复连线

### 🧐 解决方案

截图可以试试html2canvas，但是边缘超出画布的部分会显示不出来，不知道怎么解决

Start by reading the FlowEditor entry point and its current export, layout, canvas-fitting, and edge APIs. Check html2canvas for the proposed export approach, then define completion as image export including overflow, automatic layout, canvas fitting, custom edge styles, and a clear duplicate-edge rule.

Written by the indexing model from the issue text.