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/lib/types.ts

@@ -1,4 +1,5 @@
 import { TfsConfig } from '@/services/integrations/tfs';
+import { Theme } from './theme-config';
 
 // Types de base pour les tâches
 // Note: TaskStatus et TaskPriority sont maintenant gérés par la configuration centralisée dans lib/status-config.ts
@@ -13,8 +14,7 @@ export type TaskStatus =
 export type TaskPriority = 'low' | 'medium' | 'high' | 'urgent';
 export type TaskSource = 'reminders' | 'jira' | 'tfs' | 'manual';
 
-// Types de thèmes partagés
-export type Theme = 'light' | 'dark' | 'dracula' | 'monokai' | 'nord' | 'gruvbox' | 'tokyo_night' | 'catppuccin' | 'rose_pine' | 'one_dark' | 'material' | 'solarized';
+// Types de thèmes partagés - maintenant dans theme-config.ts
 
 // Interface centralisée pour les statistiques
 export interface TaskStats {