1. Make parent cards draggable with all subtasks
- Parent cards can now be dragged between columns
- All descendants are automatically moved with the parent
- Added isParent flag to drag/drop dataTransfer
2. Add Expand All / Collapse All buttons to Kanban view
- Added global expandedCards state management
- New buttons in Kanban header with ChevronsDown/Up icons
- Allows quick expansion/collapse of all parent cards
3. Add description field to tasks
- Added description textarea to TaskForm component
- Added description edit option to TaskMenu component
- Description displays in both TreeView and KanbanView
- Shows below metadata in italic gray text
- Backend already supported description field