上传组件默认值在表单内不显示

## **Describe the bug (required)** / **详细描述 bug（必填）**

A clear and concise description of what the bug is. / 请提供清晰且精确的 bug 描述
上传组件给默认值绑定数据，在表单外面会正常显示有图片， 但如果上传组件在表单里面就不会显示出默认图片~ 绑定的都是同一个变量
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## **To Reproduce (required)** / **如何复现 bug？（必填，非常重要）**

Steps to reproduce the behavior: / 详细复现步骤：

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English version example：
1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

中文版示例：
1. 打开 [demo](http://lowcode-engine.cn/demo)；
2. 点击标题；
3. 在右侧修改标题内容为「修改后的标题」；
4. 渲染画布标题组件没有更新显示为「修改后的标题」；

## **Expected behavior (required)** / **预期行为（必填，非常重要）**
A clear and concise description of what did you expect to happen. / 请清晰和精确的描述你预期的行为

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## **Screenshots (optional)** / **bug 截图（可选）**
预览的时候表单外上传有会带上默认值，表单里的上传啥也没有~

Sceenshots for further information. (If applicable.) / 一些有用的截图将会帮助我们更好的明确以及定位问题

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## **Environments (please complete the following information) (required):** / **请提供如下信息（必填）**
- AliLowCodeEngine version: [e.g. 1.0.0] / 低代码引擎版本
- AliLowCodeEngineExt version: [e.g. 1.0.0] / 低代码引擎扩展包版本
- Browser [e.g. chrome, safari] / 浏览器版本
- materials / plugins / tools / 其他物料 / 插件 / 工具链版本

> (this information can be collected via [the manual plugin](https://img.alicdn.com/imgextra/i1/O1CN0115zonY1IsgbkZ2ir7_!!6000000000949-2-tps-3066-1650.png) / 版本信息可[通过低代码用户手册插件收集](https://img.alicdn.com/imgextra/i1/O1CN0115zonY1IsgbkZ2ir7_!!6000000000949-2-tps-3066-1650.png))

## **Additional context (optional)** / **更多额外信息（可选）**
Any other context of the problem here. / 可以追加更多的额外信息，帮助定位问题

Start by reproducing the upload component with the same bound default-value variable both outside and inside a form, using the lowcode-engine demo mentioned in the issue. Compare the rendered default image in both contexts and trace the form and upload-component entry points. Done means the default image appears consistently inside and outside the form, with a regression test covering both cases.

Written by the indexing model from the issue text.