refactor: update styling and color classes across components

- Changed error message styling in ICalImportModal to use new color classes.
- Updated task completion styling in TaskListView to use new success color classes.
- Modified selected styling in ContactListItem tests to reflect new background class.
- Adjusted duplicate warning styling in ContactImportDialog to use new warning color classes.
- Refactored background and border colors in CalendarInvitationBanner for various statuses.
- Updated email list item and viewer components to use new warning and success color classes.
- Refined styling for unread indicators in email components.
- Enhanced error fallback styling in error components to use new warning color classes.
- Updated filter rule modal button hover styles to use new destructive color classes.
- Added experimental feature descriptions in Plugins and Themes settings.
- Refined vacation settings validation warning styling to use new warning color classes.
- Updated toast component styles to use new color classes for different states.
- Introduced a new built-in theme 'Qui' with specific color variables.
- Adjusted email security status colors to use new warning color classes.

components/calendar/task-list-view.tsx

@@ -204,7 +204,7 @@ export function TaskListView({
                 className={cn(
                   "mt-0.5 flex-shrink-0 w-5 h-5 rounded-full border-2 flex items-center justify-center transition-colors",
                   isCompleted
-                    ? "bg-green-500 border-green-500 text-white"
+                    ? "bg-success border-success text-success-foreground"
                     : "border-muted-foreground/40 hover:border-primary"
                 )}
                 aria-label={isCompleted ? t("tasks.mark_incomplete") : t("tasks.mark_complete")}