feat: add A2-B1 course expansion features including listening activities and conversation sessions

- Updated VocabCourseView.vue to display CEFR level for courses.
- Enhanced VocabLessonView.vue with new sections for listening activities and conversation labs, including audio controls and transcript toggling.
- Created migration to add new columns to vocab_course and new tables for conversation sessions and listening activities.
- Implemented models for vocab_conversation_session and vocab_listening_activity.
- Developed scripts to create new A2 and B1 bridge courses with structured lesson plans.
- Documented the A2-B1 expansion plan detailing course structure, learning goals, and assessment criteria.

backend/controllers/vocabController.js

@@ -84,6 +84,10 @@ class VocabController {
     this.updateGrammarExercise = this._wrapWithUser((userId, req) => this.service.updateGrammarExercise(userId, req.params.exerciseId, req.body));
     this.deleteGrammarExercise = this._wrapWithUser((userId, req) => this.service.deleteGrammarExercise(userId, req.params.exerciseId));
     this.sendLessonAssistantMessage = this._wrapWithUser((userId, req) => this.service.sendLessonAssistantMessage(userId, req.params.lessonId, req.body), { successStatus: 201 });
+    this.startConversationSession = this._wrapWithUser((userId, req) => this.service.startConversationSession(userId, req.params.lessonId, req.body), { successStatus: 201 });
+    this.sendConversationTurn = this._wrapWithUser((userId, req) => this.service.sendConversationTurn(userId, req.params.sessionId, req.body), { successStatus: 201 });
+    this.completeConversationSession = this._wrapWithUser((userId, req) => this.service.completeConversationSession(userId, req.params.sessionId));
+    this.getListeningActivities = this._wrapWithUser((userId, req) => this.service.getListeningActivities(userId, req.params.lessonId, req.query));
   }
 
   _wrapWithUser(fn, { successStatus = 200 } = {}) {