a feature to browse and select from upload image

when inserting an image, there are only options to upload a *New* image.

If an image needs to re reference in multiple places, it has to be uploaded multiple times, which is not only inconvenient, but also a wast of disk space. It's worse if during *Edit*, the linked is changed accidentally the image is forever gone.

I am wishing for an image browser of uploaded files like [wikijs ](https://js.wiki/) or [bookstack ](https://www.bookstackapp.com/). It does not have to be implemented the same the way, the existing of such a feature is more important.

该 issue 未列出文件、测试或入口点。首先定位图像插入和上传流程，然后查看链接的 Wiki.js 和 BookStack 示例，了解浏览和复用行为。完成的标准是：用户可以浏览之前上传的图像并选择一张进行插入，且不会重复上传或意外丢失。

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