refactor: update theme management and enhance UI components

- Refactored theme imports in `preferences.ts` and `ThemeSelector.tsx` to use centralized `theme-config`.
- Added new CSS variables for special cards in `globals.css` to improve theme consistency.
- Enhanced `Header` and `TaskCard` components with theme dropdown functionality for better user experience.
- Updated `ThemeProvider` to support cycling through dark themes, improving theme selection flexibility.
- Cleaned up unused imports and streamlined component structures for better maintainability.

src/actions/preferences.ts

@@ -1,7 +1,8 @@
 'use server';
 
 import { userPreferencesService } from '@/services/core/user-preferences';
-import { KanbanFilters, ViewPreferences, ColumnVisibility, TaskStatus, Theme } from '@/lib/types';
+import { KanbanFilters, ViewPreferences, ColumnVisibility, TaskStatus } from '@/lib/types';
+import { Theme } from '@/lib/theme-config';
 import { revalidatePath } from 'next/cache';
 
 /**