feat: füge Unterstützung für temporäre gap_fill-Übungen aus chapterLexemeTraining hinzu

backend/services/vocabService.js

@@ -2881,6 +2881,23 @@ export default class VocabService {
     });
 
     const plainLesson = lesson.get({ plain: true });
+    // Normalize exercise types: if question text contains clear gap placeholders,
+    // ensure the questionData.type is 'gap_fill' so the frontend renders the gap UI.
+    (plainLesson.grammarExercises || []).forEach((ex) => {
+      try {
+        const qData = typeof ex.questionData === 'string' ? JSON.parse(ex.questionData || '{}') : (ex.questionData || {});
+        const text = String(qData.text || qData.question || '').trim();
+        const hasUnderscoreGap = /_{3,}/.test(text);
+        const hasBraceGap = /\{\s*gap\s*\}/i.test(text);
+        const hasParenPlaceholders = /\(\s*_{0,}\s*\)/.test(text);
+        if ((hasUnderscoreGap || hasBraceGap || hasParenPlaceholders) && qData.type !== 'gap_fill') {
+          qData.type = 'gap_fill';
+          ex.questionData = qData;
+        }
+      } catch (err) {
+        // ignore parse errors
+      }
+    });
     
     // Lade Vokabeln aus vorherigen Lektionen (für Wiederholung UND für gemischten Vokabeltrainer)
     if (plainLesson.lessonNumber > 1) {