- Add kanban board page at /kanban with 5 status columns
(To Do, In Progress, Paused, Done, Archived)
- Use @hello-pangea/dnd for drag-and-drop between columns
- Optimistic status update on drop with API revert on failure
- Add updateTask() to tasks API client
- Task cards show title, priority badge, and truncated description
- Column headers with colored accent borders and task count badges
- Responsive: horizontal scroll with min-width 280px per column
- Loading (MosaicSpinner), error, and empty states
- All design tokens from CSS custom properties
Refs #468
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>