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/contexts/task-dialog-context.tsx

@@ -27,6 +27,7 @@ interface TaskDialogState {
   mode: 'create' | 'edit';
   task: Task | null;
   initialTemplate: TaskTemplate | null;
+  initialTask: Task | null;
   afterSubmit?: (task: Task) => void;
 }
 
@@ -41,6 +42,7 @@ interface TaskDialogAPI {
     template: TaskTemplate,
     options?: TaskDialogOptions
   ) => void;
+  openDuplicate: (task: Task, options?: TaskDialogOptions) => void;
   close: () => void;
 
   // For dialog component to call after successful operations
@@ -59,6 +61,7 @@ export function TaskDialogProvider({ children }: TaskDialogProviderProps) {
     mode: 'create',
     task: null,
     initialTemplate: null,
+    initialTask: null,
     afterSubmit: undefined,
   });
 
@@ -68,6 +71,7 @@ export function TaskDialogProvider({ children }: TaskDialogProviderProps) {
       mode: 'create',
       task: null,
       initialTemplate: null,
+      initialTask: null,
       afterSubmit: options?.onSuccess,
     });
   }, []);
@@ -78,6 +82,7 @@ export function TaskDialogProvider({ children }: TaskDialogProviderProps) {
       mode: 'edit',
       task,
       initialTemplate: null,
+      initialTask: null,
       afterSubmit: options?.onSuccess,
     });
   }, []);
@@ -89,6 +94,21 @@ export function TaskDialogProvider({ children }: TaskDialogProviderProps) {
         mode: 'create',
         task: null,
         initialTemplate: template,
+        initialTask: null,
+        afterSubmit: options?.onSuccess,
+      });
+    },
+    []
+  );
+
+  const openDuplicate = useCallback(
+    (sourceTask: Task, options?: TaskDialogOptions) => {
+      setDialogState({
+        isOpen: true,
+        mode: 'create',
+        task: null,
+        initialTemplate: null,
+        initialTask: sourceTask,
         afterSubmit: options?.onSuccess,
       });
     },
@@ -119,10 +139,19 @@ export function TaskDialogProvider({ children }: TaskDialogProviderProps) {
       openCreate,
       openEdit,
       openFromTemplate,
+      openDuplicate,
       close,
       handleSuccess,
     }),
-    [dialogState, openCreate, openEdit, openFromTemplate, close, handleSuccess]
+    [
+      dialogState,
+      openCreate,
+      openEdit,
+      openFromTemplate,
+      openDuplicate,
+      close,
+      handleSuccess,
+    ]
   );
 
   return (