Enhance logging and conditional rendering in VocabService and VocabLessonView

- Added detailed logging in VocabService for lesson retrieval, including lesson ID, title, and exercise count.
- Improved conditional rendering in VocabLessonView to handle cases where grammar exercises may not be present, enhancing user experience.
- Updated logging in VocabLessonView to provide insights into loaded lessons and exercises, aiding in debugging and monitoring.

debug-lesson-exercises.js

@@ -0,0 +1,78 @@
+#!/usr/bin/env node
+/**
+ * Debug-Script zum Prüfen, ob Übungen für eine Lektion vorhanden sind
+ * Verwendung: node debug-lesson-exercises.js [lessonId]
+ */
+
+import { sequelize } from './backend/utils/sequelize.js';
+import VocabCourseLesson from './backend/models/community/vocab_course_lesson.js';
+import VocabGrammarExercise from './backend/models/community/vocab_grammar_exercise.js';
+
+const lessonId = process.argv[2] ? parseInt(process.argv[2]) : 1;
+
+async function debugLesson() {
+  try {
+    await sequelize.authenticate();
+    console.log('✅ Datenbankverbindung erfolgreich\n');
+
+    // Lade Lektion mit Übungen (wie im Backend)
+    const lesson = await VocabCourseLesson.findByPk(lessonId, {
+      include: [
+        {
+          model: require('./backend/models/community/vocab_course.js').default,
+          as: 'course'
+        },
+        {
+          model: VocabGrammarExercise,
+          as: 'grammarExercises',
+          include: [
+            {
+              model: require('./backend/models/community/vocab_grammar_exercise_type.js').default,
+              as: 'exerciseType'
+            }
+          ],
+          required: false,
+          separate: true,
+          order: [['exerciseNumber', 'ASC']]
+        }
+      ]
+    });
+
+    if (!lesson) {
+      console.log(`❌ Lektion ${lessonId} nicht gefunden`);
+      return;
+    }
+
+    console.log(`📚 Lektion: ${lesson.title} (ID: ${lesson.id})`);
+    console.log(`   Kurs: ${lesson.course?.title || 'N/A'}`);
+    console.log(`   Übungen (via Include): ${lesson.grammarExercises ? lesson.grammarExercises.length : 0}\n`);
+
+    // Prüfe direkt in der Datenbank
+    const directExercises = await VocabGrammarExercise.findAll({
+      where: { lessonId: lesson.id },
+      order: [['exerciseNumber', 'ASC']]
+    });
+
+    console.log(`📊 Direkte Abfrage: ${directExercises.length} Übung(en) gefunden`);
+    directExercises.forEach((ex, idx) => {
+      console.log(`   ${idx + 1}. ${ex.title} (ID: ${ex.id}, Typ: ${ex.exerciseTypeId})`);
+    });
+
+    // Plain object
+    const plain = lesson.get({ plain: true });
+    console.log(`\n📦 Plain Object:`);
+    console.log(`   grammarExercises: ${plain.grammarExercises ? plain.grammarExercises.length : 'undefined'}`);
+    if (plain.grammarExercises && plain.grammarExercises.length > 0) {
+      plain.grammarExercises.forEach((ex, idx) => {
+        console.log(`   ${idx + 1}. ${ex.title} (ID: ${ex.id})`);
+      });
+    }
+
+  } catch (error) {
+    console.error('❌ Fehler:', error);
+  } finally {
+    await sequelize.close();
+  }
+}
+
+debugLesson();