fix(frontend): Implement Task Edit functionality - Sprint 4 Story 2

Completed the missing Task Edit feature identified as high-priority
issue in Sprint 4 testing.

Changes:
- Created TaskEditDialog component (285 lines)
  - Full form with title, description, priority, hours fields
  - React Hook Form + Zod validation
  - Modal dialog with proper UX (loading states, error handling)
  - Support for all Task fields (estimated/actual hours)
- Integrated TaskEditDialog into TaskCard component
  - Added isEditDialogOpen state management
  - Connected Edit menu item to open dialog
  - Proper event propagation handling

Features:
- Complete CRUD: Users can now edit existing tasks
- Form validation with clear error messages
- Optimistic updates via React Query
- Toast notifications for success/error
- Responsive design matches existing UI

Testing:
- Frontend compiles successfully with no errors
- Component follows existing patterns (Story Form, Task Quick Add)
- Consistent with shadcn/ui design system

Fixes: Task Edit TODO at task-card.tsx:147
Related: Sprint 4 Story 2 - Task Management
Test Report: SPRINT_4_STORY_1-3_FRONTEND_TEST_REPORT.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/tasks/task-card.tsx

@@ -23,6 +23,7 @@ import {
   Circle
 } from 'lucide-react';
 import { cn } from '@/lib/utils';
+import { TaskEditDialog } from './task-edit-dialog';
 
 interface TaskCardProps {
   task: Task;
@@ -45,6 +46,7 @@ const statusColors = {
 
 export function TaskCard({ task, storyId }: TaskCardProps) {
   const [isExpanded, setIsExpanded] = useState(false);
+  const [isEditDialogOpen, setIsEditDialogOpen] = useState(false);
   const changeStatus = useChangeTaskStatus();
   const updateTask = useUpdateTask();
   const deleteTask = useDeleteTask();
@@ -144,7 +146,7 @@ export function TaskCard({ task, storyId }: TaskCardProps) {
                 </Button>
               </DropdownMenuTrigger>
               <DropdownMenuContent align="end">
-                <DropdownMenuItem onClick={() => {/* TODO: Open edit dialog */}}>
+                <DropdownMenuItem onClick={() => setIsEditDialogOpen(true)}>
                   <Pencil className="w-4 h-4 mr-2" />
                   Edit
                 </DropdownMenuItem>
@@ -160,6 +162,13 @@ export function TaskCard({ task, storyId }: TaskCardProps) {
           </div>
         </div>
       </CardHeader>
+
+      {/* Edit Dialog */}
+      <TaskEditDialog
+        task={task}
+        open={isEditDialogOpen}
+        onOpenChange={setIsEditDialogOpen}
+      />
     </Card>
   );
 }