[Feature] Migrate image/file upload feature from CoPaw to WebUI

## Problem Description
Currently webui does not support uploading images or files.
This feature is already in CoPaw: https://github.com/agentscope-ai/CoPaw/pull/1772

## Proposed Solution
Add similar features from CoPaw to webui

## Affected Component(s)
- [ ] Engine
- [ ] Sandbox
- [ ] Common
- [ ] Tools
- [ ] Documentation
- [x] Other: _webui__________

## Alternatives Considered
[Describe any alternative solutions you've considered]

## Additional Context
[Any other context, screenshots, or examples about the feature request]