- Add backend file operations (copy, move, delete, rename, download) in file-service.ts with workspace root protection
- Add API routes for file operations including directory download as zip via archiver
- Add client API functions in api.ts for all file operation endpoints
- Add context menu UI in FileBrowser component with operations dialog for confirming destructive actions
- Add CSS styles for context menu including danger items and dividers
- Add 33 FileBrowser context menu tests and 485+ file-service tests
- Fix pre-existing test failures in routes-diff, mission-e2e, and theme sync tests
- Add server-side file service with list, read, and write operations
- Add REST API endpoints for file operations with tests
- Add client-side API functions and React hooks for file browsing
- Create FileBrowser, FileEditor, and FileBrowserModal components
- Add CodeMirror 6 for syntax-highlighted file editing
- Integrate Files tab into TaskDetailModal
- Add comprehensive file browser styles and responsive design
