refactor(task-list): enhance task row components with depth handling

- Added depth and maxDepth props to TaskRow, TaskRowWithSubtasks, and TitleColumn components to manage nested subtasks more effectively.
- Updated AddSubtaskRow to support depth for proper indentation and visual hierarchy.
- Improved styling for subtasks based on their depth level, ensuring better visual distinction.
- Adjusted task management slice to utilize actual subtask counts from the backend for accurate display.

worklenz-frontend/src/features/task-management/task-management.slice.ts

@@ -1010,7 +1010,7 @@ const taskManagementSlice = createSlice({
             order: subtask.sort_order || subtask.order || 0,
             parent_task_id: parentTaskId,
             is_sub_task: true,
-            sub_tasks_count: 0,
+            sub_tasks_count: subtask.sub_tasks_count || 0, // Use actual count from backend
             show_sub_tasks: false,
           }));