feat(routes): implement lazy loading and suspense fallback for route components

- Refactored account setup, admin center, reporting, and settings routes to utilize React's lazy loading for improved performance.
- Wrapped route components in Suspense with a fallback UI to enhance user experience during loading states.
- Removed unused drag-and-drop CSS file to clean up the codebase.

worklenz-frontend/src/components/task-management/task-list-board.tsx

@@ -27,6 +27,8 @@ import {
   fetchTasksV3,
   selectTaskGroupsV3,
   selectCurrentGroupingV3,
+  fetchSubTasks,
+  toggleTaskExpansion,
 } from '@/features/task-management/task-management.slice';
 import {
   selectTaskGroups,