Add lesson retrieval functionality in VocabController and VocabService

- Introduced a new method in VocabService to fetch lesson details, including access control based on user ownership and lesson visibility.
- Updated VocabController to wrap the new method for user access.
- Added a new route in VocabRouter to handle requests for specific lessons.
- Enhanced VocabCourseListView to support navigation to individual lesson views, improving user experience in accessing lesson content.

frontend/src/views/social/VocabCourseListView.vue

@@ -197,6 +197,10 @@ export default {
           const nativeLang = this.languages.find(lang => lang.name === nativeLanguageName);
           if (nativeLang) {
             this.myNativeLanguageId = nativeLang.id;
+            // Setze die eigene Muttersprache als Standardauswahl
+            if (!this.selectedNativeLanguageId) {
+              this.selectedNativeLanguageId = 'my';
+            }
             console.log(`[loadMyNativeLanguageId] Gefunden: ${nativeLanguageName} (ID: ${nativeLang.id})`);
           } else {
             console.warn(`[loadMyNativeLanguageId] Sprache "${nativeLanguageName}" nicht in languages-Liste gefunden. Verfügbare Sprachen:`, this.languages.map(l => l.name).join(', '));
@@ -297,6 +301,16 @@ export default {
         this.loading = false;
       }
     },
+    async checkIfHasCourses() {
+      // Prüfe, ob der Benutzer bereits Kurse hat
+      try {
+        const res = await apiClient.get('/api/vocab/courses/my');
+        const courses = res.data || [];
+        return courses.length > 0;
+      } catch (e) {
+        return false;
+      }
+    },
     async createCourse() {
       try {
         await apiClient.post('/api/vocab/courses', this.newCourse);
@@ -318,7 +332,8 @@ export default {
     async enroll(courseId) {
       try {
         await apiClient.post(`/api/vocab/courses/${courseId}/enroll`);
-        await this.loadAllCourses();
+        // Nach dem Einschreiben sofort zum Kurs navigieren
+        this.openCourse(courseId);
       } catch (e) {
         console.error('Fehler beim Einschreiben:', e);
         alert(e.response?.data?.error || 'Fehler beim Einschreiben');
@@ -333,7 +348,13 @@ export default {
   },
   async mounted() {
     await this.loadLanguages();
-    await this.loadAllCourses();
+    // Wenn der Benutzer bereits Kurse hat, zeige "Meine Kurse" als Standard
+    const hasCourses = await this.checkIfHasCourses();
+    if (hasCourses) {
+      await this.loadMyCourses();
+    } else {
+      await this.loadAllCourses();
+    }
   },
 };
 </script>