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/contacts/contact-list-item.tsx

@@ -59,9 +59,9 @@ export function ContactListItem({ contact, isSelected, isChecked, hasSelection,
       className={cn(
         "w-full flex items-center cursor-pointer select-none transition-all duration-200 border-b border-border",
         isSelected
-          ? "bg-blue-200 dark:bg-blue-900/50 shadow-sm"
+          ? "bg-selection shadow-sm"
           : "bg-background hover:bg-muted hover:shadow-sm",
-        isChecked && !isSelected && "ring-2 ring-primary/20 bg-blue-100 dark:bg-blue-900/30",
+        isChecked && !isSelected && "ring-2 ring-primary/20 bg-selection/60",
       )}
       style={{ gap: 'var(--density-item-gap)', paddingInline: '16px', paddingBlock: 'var(--density-item-py)' }}
     >