feat(kanban): implement portal for delete confirmation modal

- Introduced a Portal component to render the delete confirmation modal outside the main DOM hierarchy, improving UI responsiveness.
- Updated the delete confirmation modal to utilize the Portal for better overlay management and user experience.
- Enhanced styling and interaction handling for the modal, ensuring it aligns with the application's theme and accessibility standards.

worklenz-frontend/src/components/enhanced-kanban/EnhancedKanbanBoardNativeDnD/KanbanGroup.tsx

@@ -24,7 +24,13 @@ import {
     fetchEnhancedKanbanGroups,
     IGroupBy,
 } from '@/features/enhanced-kanban/enhanced-kanban.slice';
+import { createPortal } from 'react-dom';
 
+// Simple Portal component
+const Portal: React.FC<{ children: React.ReactNode }> = ({ children }) => {
+    const portalRoot = document.getElementById('portal-root') || document.body;
+    return createPortal(children, portalRoot);
+};
 
 interface KanbanGroupProps {
     group: ITaskListGroup;
@@ -414,8 +420,15 @@ const KanbanGroup: React.FC<KanbanGroupProps> = memo(({
 
                 {/* Simple Delete Confirmation */}
                 {showDeleteConfirm && (
-                    <div className="fixed inset-0 bg-black bg-opacity-25 flex items-center justify-center z-50">
-                        <div className="bg-white dark:bg-gray-800 rounded-lg shadow-lg border border-gray-200 dark:border-gray-700 max-w-sm w-full mx-4">
+                    <Portal>
+                        <div 
+                            className="fixed inset-0 bg-black bg-opacity-25 flex items-center justify-center z-[99999]"
+                            onClick={() => setShowDeleteConfirm(false)}
+                        >
+                            <div 
+                                className="bg-white dark:bg-gray-800 rounded-lg shadow-lg border border-gray-200 dark:border-gray-700 max-w-sm w-full mx-4"
+                                onClick={e => e.stopPropagation()}
+                            >
                                 <div className="p-4">
                                     <div className="flex items-center gap-3 mb-3">
                                         <div className="flex-shrink-0">
@@ -454,6 +467,7 @@ const KanbanGroup: React.FC<KanbanGroupProps> = memo(({
                                 </div>
                             </div>
                         </div>
+                    </Portal>
                 )}
                 <div className="enhanced-kanban-group-tasks">
                     {/* Create card at top */}