Implement vocab course and grammar exercise features in backend and frontend

- Added new course management functionalities in VocabController, including creating, updating, and deleting courses and lessons.
- Implemented enrollment and progress tracking for courses, along with grammar exercise creation and management.
- Updated database schema to include tables for courses, lessons, enrollments, and grammar exercises.
- Enhanced frontend with new routes and views for course listing and details, including internationalization support for course-related texts.
- Improved user experience by adding navigation to courses from the main vocab trainer view.

frontend/src/views/social/VocabTrainerView.vue

@@ -6,6 +6,7 @@
 
     <div class="actions">
       <button @click="goNewLanguage">{{ $t('socialnetwork.vocab.newLanguage') }}</button>
+      <button @click="goCourses">{{ $t('socialnetwork.vocab.courses.title') }}</button>
     </div>
 
     <div v-if="loading">{{ $t('general.loading') }}</div>
@@ -43,6 +44,9 @@ export default {
     goNewLanguage() {
       this.$router.push('/socialnetwork/vocab/new');
     },
+    goCourses() {
+      this.$router.push('/socialnetwork/vocab/courses');
+    },
     openLanguage(id) {
       this.$router.push(`/socialnetwork/vocab/${id}`);
     },