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/__tests__/contact-list-item.test.tsx

@@ -52,7 +52,7 @@ describe('ContactListItem', () => {
   it('applies selected styling', () => {
     const { container } = render(<ContactListItem contact={contact} {...baseProps} isSelected={true} />);
     const div = container.firstElementChild;
-    expect(div?.className).toContain('bg-blue-200');
+    expect(div?.className).toContain('bg-selection');
   });
 
   it('shows email as display name when no name exists', () => {

components/contacts/contact-import-dialog.tsx

@@ -205,7 +205,7 @@ export function ContactImportDialog({
                       )}
                     </div>
                     {isDupe && (
-                      <span className="text-xs px-1.5 py-0.5 rounded bg-amber-100 dark:bg-amber-900 text-amber-700 dark:text-amber-400 flex-shrink-0">
+                      <span className="text-xs px-1.5 py-0.5 rounded bg-warning/15 text-warning flex-shrink-0">
                         {t("import.duplicate")}
                       </span>
                     )}

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)' }}
     >