[Feature] 导出知识库，导入后能否支持源文件下载

### MaxKB Version

2.9.2

### Please describe your needs or suggestions for improvements

目前客户通过到处知识库进行知识库的迁移，发现导入后的知识库无法下载源文件。能否优化下，支持源文件下载

<img width="3827" height="1911" alt="Image" src="https://github.com/user-attachments/assets/73c122ae-c963-4329-b888-d0787b56c24e" />

### Please describe the solution you suggest

_No response_

### Additional Information

_No response_