### TL;DR
feat: optimize workspace attachment uploading & error display

### What Changes
####
Support for Workspace Attachment Uploading & Error Handling
* Added support for three attachment states: uploading (local), upload failed (local error), and uploaded (persisted). The frontend UI now displays real-time upload progress and error messages.
* Attachments that fail to upload can be deleted directly without confirmation.
* Merged display of uploading and uploaded attachments for a smoother user experience.
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **New Features**
- Attachments now show real-time upload status including uploading, error, and uploaded states.
- Users can remove failed (error) attachments instantly without confirmation.
- Attachment list merges uploading and uploaded files, displaying up to 10 items.
- **Bug Fixes**
- Improved error handling and messaging for failed attachment uploads.
- **Style**
- Enhanced visual styling for error attachments with distinct colors and backgrounds.
- **Tests**
- Added tests simulating slow network uploads, upload failures, and direct removal of error attachments.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->