Add duplicate task button (vibe-kanban) (#593)

* ## ✅ Implementation Complete!

I've successfully implemented the duplicate task feature. Here's what was accomplished:

### **Changes Made:**

1. **TaskDialogContext (`frontend/src/contexts/task-dialog-context.tsx`)**
   - Added `initialTask: Task | null` to dialog state
   - Created `openDuplicate(task, options)` method that opens create dialog with initial data
   - Updated all existing methods to include initialTask field

2. **TaskFormDialog (`frontend/src/components/tasks/TaskFormDialog.tsx`)**
   - Added `initialTask?: Task | null` prop
   - Enhanced prefill logic with priority: Edit → Duplicate → Template → Empty
   - Duplicated tasks reset status to 'todo' and start with no images

3. **TaskCard (`frontend/src/components/tasks/TaskCard.tsx`)**
   - Added Copy icon import
   - Added `onDuplicate?: (task: Task) => void` prop
   - Added "Duplicate" menu item with Copy icon between Edit and Delete

4. **TaskKanbanBoard (`frontend/src/components/tasks/TaskKanbanBoard.tsx`)**
   - Added `onDuplicateTask?: (task: Task) => void` prop
   - Passed duplicate handler through to TaskCard components

5. **ProjectTasks (`frontend/src/pages/project-tasks.tsx`)**
   - Added `openDuplicate` to useTaskDialog destructuring
   - Created `handleDuplicateTask` function
   - Passed duplicate handler to TaskKanbanBoard

6. **TaskFormDialogContainer (`frontend/src/components/tasks/TaskFormDialogContainer.tsx`)**
   - Added `initialTask={dialogState.initialTask}` prop to TaskFormDialog

### **How It Works:**

1. **User clicks** the "⋯" menu on any task card
2. **Sees "Duplicate"** option with copy icon between Edit and Delete
3. **Clicks Duplicate** → opens create task dialog with:
   - Title and description pre-filled from original task
   - Status reset to 'todo'
   - No images (clean slate)
   - User can modify and create as normal

### **Key Design Decisions:**
- **Treated as create mode** (not edit) - follows Oracle's recommendation
- **Status always resets to 'todo'** for duplicated tasks
- **No images copied** - simple and safe approach
- **Clean integration** with existing template system

The implementation passes all TypeScript checks and follows the existing codebase patterns. The feature is ready to use!

* Cleanup script changes for task attempt 16b21999-278c-414d-aaab-ae5767d42d77

frontend/src/pages/project-tasks.tsx

@@ -45,7 +45,7 @@ export function ProjectTasks() {
   const [project, setProject] = useState<Project | null>(null);
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
-  const { openCreate, openEdit } = useTaskDialog();
+  const { openCreate, openEdit, openDuplicate } = useTaskDialog();
   const [isProjectSettingsOpen, setIsProjectSettingsOpen] = useState(false);
   const { query: searchQuery } = useSearch();
 
@@ -187,6 +187,13 @@ export function ProjectTasks() {
     [openEdit]
   );
 
+  const handleDuplicateTask = useCallback(
+    (task: Task) => {
+      openDuplicate(task);
+    },
+    [openDuplicate]
+  );
+
   const handleViewTaskDetails = useCallback(
     (task: Task, attemptIdToShow?: string) => {
       // setSelectedTask(task);
@@ -336,6 +343,7 @@ export function ProjectTasks() {
               onDragEnd={handleDragEnd}
               onEditTask={handleEditTask}
               onDeleteTask={handleDeleteTask}
+              onDuplicateTask={handleDuplicateTask}
               onViewTaskDetails={handleViewTaskDetails}
               isPanelOpen={isPanelOpen}
             />