Kanban Board

Create a Kanban board component with:

## Board Layout
- Horizontal columns: To Do, In Progress, In Review, Done
- Column headers with task count and "Add Task" button
- Cards draggable between columns (drag and drop)
- Smooth drag animation with visual drop zone indicator

## Task Cards
- Title (editable inline on click)
- Priority indicator: 🔴 High, 🟡 Medium, 🟢 Low
- Assignee avatars (up to 3, with +N overflow)
- Due date badge (red if overdue)
- Label tags (Feature, Bug, Enhancement) with colors
- Subtask progress: "3/5 subtasks"
- Comment count icon

## Features
- Add new column with custom name
- Add new task with modal: Title, Description, Priority, Assignee, Due Date, Labels
- Filter tasks by: assignee, priority, label
- Search across all cards
- Column collapse/expand toggle
- Card click opens detail view in side panel

## Detail Side Panel
- Full task title and description (markdown support)
- Assignee selector
- Due date picker
- Label management
- Subtask checklist
- Activity log / comments

Use shadcn/ui components. Clean design with subtle card shadows. Responsive — stack columns vertically on mobile.