refactor(vocabService, VocabLessonView): unify answer language classification for multiple-choice questions

- Renamed and refactored the method for classifying answer languages in multiple-choice questions from _classifyMcQuestionSide to _resolveMcAnswerSide for clarity and consistency.
- Updated the logic to classify answer languages based on questionData.answerLanguage and answerLanguageId, improving accuracy in determining the correct language context.
- Adjusted VocabLessonView to utilize the new classification method, ensuring alignment with backend changes and enhancing the handling of distractor options based on answer language.
- Enhanced documentation to clarify the expected input and output for the new method, improving maintainability and understanding of the codebase.

backend/services/vocabService.js

@@ -3593,20 +3593,30 @@ export default class VocabService {
   }
 
   /**
-   * Ordnet eine Multiple-Choice-Frage der Zielsprache (zu lernen) oder Muttersprache (Erklärung) zu,
-   * damit Distraktoren aus dem passenden Wortpool gewählt werden können.
+   * Explizite Zuordnung der Antwortsprache (sprachneutral).
+   * questionData.answerLanguage: 'target' | 'native'
+   * oder questionData.answerLanguageId: 1 = target (Lernsprache), 2 = native (Muttersprache)
+   * Ohne diese Felder: 'unknown' (kein Eintrag in den Distraktor-Pools für diese Frage).
+   * @param {object} questionData
    * @returns {'target'|'native'|'unknown'}
    */
-  _classifyMcQuestionSide(question) {
-    const q = String(question || '');
-    if (/Wie sagt man\s/i.test(q) || /Übersetze/i.test(q)) return 'target';
-    if (/Was bedeutet/i.test(q)) return 'native';
+  _resolveMcAnswerSide(questionData) {
+    if (!questionData || typeof questionData !== 'object') return 'unknown';
+    const raw = questionData.answerLanguage;
+    if (typeof raw === 'string') {
+      const s = raw.trim().toLowerCase();
+      if (s === 'target' || s === 'learning' || s === 'l2') return 'target';
+      if (s === 'native' || s === 'l1') return 'native';
+    }
+    const id = questionData.answerLanguageId;
+    if (id === 1 || id === '1') return 'target';
+    if (id === 2 || id === '2') return 'native';
     return 'unknown';
   }
 
   /**
    * Sammelt Vokabeln aus allen Multiple-Choice-Übungen von Lektionen **vor** der angegebenen Lektion
-   * (gleicher Kurs), getrennt nach Ziel- vs. Muttersprache anhand der Frageformulierung.
+   * (gleicher Kurs), getrennt nach Ziel- vs. Muttersprache anhand von answerLanguage / answerLanguageId.
    */
   async getVocabDistractorPool(hashedUserId, courseId, beforeLessonId) {
     if (!beforeLessonId) {
@@ -3659,10 +3669,9 @@ export default class VocabService {
     for (const ex of exercises) {
       const qd =
         typeof ex.questionData === 'string' ? JSON.parse(ex.questionData) : ex.questionData;
-      const question = qd?.question || '';
       const opts = qd?.options;
       if (!Array.isArray(opts)) continue;
-      const side = this._classifyMcQuestionSide(question);
+      const side = this._resolveMcAnswerSide(qd);
       if (side === 'target') {
         opts.forEach((o) => target.add(String(o).trim()));
       } else if (side === 'native') {