Enhance VocabService logging and update VocabCourseListView state management

- Added debug logging in VocabService to track course retrieval details, aiding in troubleshooting and performance monitoring.
- Updated VocabCourseListView to include additional state properties for managing share codes and search functionality, improving user experience and interaction capabilities.

frontend/src/views/social/VocabCourseListView.vue

@@ -141,10 +141,17 @@ export default {
       courses: [],
       languages: [],
       showCreateDialog: false,
+      showShareCodeDialog: false,
+      searchTerm: '',
+      selectedLanguageId: '',
+      selectedNativeLanguageId: '',
+      shareCode: '',
+      searchTimeout: null,
       newCourse: {
         title: '',
         description: '',
         languageId: null,
+        nativeLanguageId: null,
         difficultyLevel: 1,
         isPublic: false
       }