fix: update scheduler filesystem path from .kb to .fusion for task validation
style: clean up TaskDetailModal styling with reusable CSS classes
test: add comprehensive tests for file-service operations with mocked filesystem
- Add 'archived' column to task store with archiveTask and unarchiveTask methods
- Add CLI commands: kb task archive <id> and kb task unarchive <id>
- Add pi extension tools for archive and unarchive operations
- Add dashboard API endpoints POST /api/tasks/:id/archive and /unarchive
- Add Archived column to board UI with archive/unarchive buttons
- Prevent drag-drop into archived column, add visual distinction
- Include duplicateTask from concurrent branch in merge resolution
- Change desktop .column min-width from 260px to 0, letting the grid control sizing
- Add overflow-x: hidden to .column-body to prevent content blowout
- Use fixed width: 280px for mobile columns instead of min-width
- Add column-fixed-width tests verifying CSS constraints for desktop and mobile
