feat(filesystem): add file upload with progress tracking and folder caching
- Fix broken SDK pagination by using direct API calls for folder listing
- Cache folder ID in local storage to avoid expensive searches on reload
- Implement file upload using direct API instead of broken SDK method
- Add upload progress UI with status messages in Files sidebar
- Handle job polling with 404 fallback for instant completions
- Add MemoryBlockViewer component for desktop/mobile viewing
- Add developer mode with agent refresh capability
- Improve error logging throughout streaming and upload flows