Kanban Board

Create a kanban board with 4 columns: Backlog, To Do, In Progress, and Done. Each column contains draggable task cards with title, description, assignee avatar, priority badge (Low, Medium, High), and due date. Include an "Add task" button per column. Use shadcn/ui Card, Badge, Avatar, and Button components, plus Tailwind CSS. Implement drag-and-drop between columns and responsive horizontal scrolling. Make cards keyboard focusable.

创建一个包含 4 列的看板：Backlog、To Do、In Progress 和 Done。每列包含可拖拽的任务卡片，包含标题、描述、负责人头像、优先级徽章（Low、Medium、High）和截止日期。每列包含 "Add task" 按钮。使用 shadcn/ui Card、Badge、Avatar 和 Button 组件以及 Tailwind CSS。实现列之间的拖放和响应式水平滚动。使卡片支持键盘聚焦。