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/email/smime-status-banner.tsx

@@ -83,10 +83,10 @@ export function SmimeStatusBanner({ status, onUnlockKey, className }: SmimeStatu
   if (items.length === 0) return null;
 
   const variantStyles = {
-    success: 'bg-green-50 dark:bg-green-950/30 text-green-700 dark:text-green-400 border-green-200 dark:border-green-800',
-    warning: 'bg-yellow-50 dark:bg-yellow-950/30 text-yellow-700 dark:text-yellow-400 border-yellow-200 dark:border-yellow-800',
-    error: 'bg-red-50 dark:bg-red-950/30 text-red-700 dark:text-red-400 border-red-200 dark:border-red-800',
-    info: 'bg-blue-50 dark:bg-blue-950/30 text-blue-700 dark:text-blue-400 border-blue-200 dark:border-blue-800',
+    success: 'bg-success/10 text-success border-success/30',
+    warning: 'bg-warning/10 text-warning border-warning/30',
+    error: 'bg-destructive/10 text-destructive border-destructive/30',
+    info: 'bg-info/10 text-info border-info/30',
   };
 
   return (