feat(vocab): add dashboard learning summary and related endpoints

- Introduced `getDashboardLearningSummary` method in `VocabService` to provide a compact overview of enrolled courses and current lessons for users.
- Updated `vocabController` to include a new route for the dashboard widget, allowing users to access their learning summary.
- Enhanced `vocabRouter` to route requests for the new dashboard widget endpoint.
- Added localization support for the new dashboard features across multiple languages, improving user engagement and accessibility.
- Updated UI components to integrate the new dashboard widget, ensuring a seamless user experience.

backend/routers/vocabRouter.js

@@ -7,6 +7,8 @@ const vocabController = new VocabController();
 
 router.use(authenticate);
 
+router.get('/dashboard-widget', vocabController.getDashboardLearningSummary);
+
 router.get('/languages', vocabController.listLanguages);
 router.get('/languages/all', vocabController.listAllLanguages);
 router.post('/languages', vocabController.createLanguage);