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.

frontend/src/i18n/locales/ceb/home.json

@@ -23,7 +23,8 @@
         "news": "Balita",
         "birthdays": "Mga adlawng natawhan",
         "upcoming": "Umaabot nga mga appointment",
-        "calendar": "Kalendaryo"
+        "calendar": "Kalendaryo",
+        "vocabCourses": "Mga kurso sa pinulongan"
       },
       "overview": {
         "activeWidgetsLabel": "Aktibong mga widget",