feat: add updatedAt field to AchievementCard and related services

- Introduced `updatedAt` property in `AchievementData`, `KeyAccomplishment`, and `Task` interfaces for improved task tracking.
- Updated `AchievementCard` UI to display the last updated date alongside completion date, enhancing user visibility.
- Adjusted `UIShowcaseClient` and `TasksService` to include `updatedAt` values, ensuring consistency across task management components.

src/components/ui-showcase/UIShowcaseClient.tsx

@@ -64,6 +64,7 @@ export function UIShowcaseClient() {
       description: 'Migration vers les composants UI génériques',
       impact: 'high',
       completedAt: new Date(),
+      updatedAt: new Date(),
       tags: ['refactoring', 'ui'],
       todosCount: 8
     },
@@ -73,6 +74,7 @@ export function UIShowcaseClient() {
       description: 'Ajout de 10 nouveaux thèmes avec CSS variables',
       impact: 'medium',
       completedAt: new Date(Date.now() - 86400000),
+      updatedAt: new Date(Date.now() - 86400000),
       tags: ['themes', 'css'],
       todosCount: 3
     }