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/thread-email-item.tsx

@@ -85,9 +85,9 @@ export function ThreadEmailItem({
         "pl-12 pr-4",
         "border-l-2 border-l-transparent",
         selected
-          ? "bg-blue-200 dark:bg-blue-900/50 border-l-primary"
+          ? "bg-selection border-l-primary"
           : "hover:bg-muted/50",
-        isUnread && !selected && "bg-amber-50 dark:bg-amber-900/20",
+        isUnread && !selected && "bg-warning/10",
         !isLast && "border-b border-border/30",
         isChecked && "ring-2 ring-primary/20 bg-accent/40",
         isDragging && "opacity-50 scale-[0.98] ring-2 ring-primary/30",
@@ -121,7 +121,7 @@ export function ThreadEmailItem({
         {/* Unread indicator */}
         {isUnread && (
           <div className="absolute left-7 top-1/2 -translate-y-1/2">
-            <Circle className="w-1.5 h-1.5 fill-blue-600 text-blue-600 dark:fill-blue-400 dark:text-blue-400" />
+            <Circle className="w-1.5 h-1.5 fill-unread text-unread" />
           </div>
         )}