Feature: 希望沙盒里可以实现文字和图片一起发送，以及在沙盒里增加一个上传本地图片的按钮

### Describe the problem related to the feature request

比如novelai插件，rryth插件，识图和搜图插件等，这些插件需要图片和文字一起发送，比如novelai插件的图生图功能需要：约稿+图片。如果沙盒里可以支持文字和图片一起发送，用户可以更好地在本地测试这些插件的功能。
文字和图片一起发送，就像这样：

### Describe the solution you'd like

比如说在沙盒中，可以粘贴或上传图片到输入框，并支持和文字一起发送

### Describe alternatives you've considered

暂无

### Additional context

暂无

Start by locating the sandbox input and its existing text-message send flow. Check how the sandbox currently handles pasted or selected content; done means a user can paste or upload a local image, include text, and send both together for plugin testing.

Written by the indexing model from the issue text.