feat(AssigneeSelector): add kanbanMode prop for enhanced task assignment

- Introduced kanbanMode prop to AssigneeSelector and LazyAssigneeSelectorWrapper for improved functionality in Kanban view.
- Updated EnhancedKanbanTaskCard and TaskCard components to utilize the new kanbanMode prop.
- Adjusted task sorting logic to handle cases where sort_order may be undefined, ensuring robust behavior during task updates.

worklenz-frontend/src/components/enhanced-kanban/EnhancedKanbanTaskCard.tsx

@@ -182,11 +182,7 @@ const EnhancedKanbanTaskCard: React.FC<EnhancedKanbanTaskCardProps> = React.memo
                 isDarkMode={themeMode === 'dark'}
                 size={24}
               />
-              <LazyAssigneeSelectorWrapper
-                task={task}
-                groupId={sectionId}
-                isDarkMode={themeMode === 'dark'}
-              />
+              <LazyAssigneeSelectorWrapper task={task} groupId={sectionId} isDarkMode={themeMode === 'dark'} kanbanMode={true} />
             </Flex>
             <Flex gap={4} align="center">
               <CustomDueDatePicker task={task} onDateChange={setDueDate} />