### What problem does this PR solve?
Update **Chat** UI:
- Align to the design.
- Update `<AudioButton>` visualizer logic.
- Fix keyboard navigation issue.
### Type of change
- [x] Refactoring
## Summary
- keep assistant message containers stretched to available width
- avoid width collapse during streaming by allowing flex items to shrink
## Test plan
- not run (not requested)
Fixes#12985
Made with [Cursor](https://cursor.com)
Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Liu An <asiro@qq.com>
### What problem does this PR solve?
Refactor: UmiJs -> Vite+React
### Type of change
- [x] Refactoring
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Co-authored-by: Liu An <asiro@qq.com>
