feat(vocabLesson): add detailed review section for failed chapter exams

- Introduced a new review section that displays questions, user answers, and correct answers for failed chapter exams.
- Added localization entries for the review section in multiple languages, enhancing user experience and understanding of mistakes.
- Implemented logic to format and present failed exam details, improving feedback for learners.

frontend/src/views/social/VocabLessonView.vue

@@ -957,6 +957,25 @@
           target: exerciseTargetScore,
           count: exerciseRetryUnlockAttempts
         }) }}</p>
+        <div v-if="chapterExamFailedDetails.length > 0" class="exam-failed-review">
+          <h4>{{ $t('socialnetwork.vocab.courses.exerciseExamFailedReviewTitle') }}</h4>
+          <ul>
+            <li v-for="(item, index) in chapterExamFailedDetails" :key="`failed-${index}-${item.id}`">
+              <p class="exam-failed-review__question">
+                <strong>{{ $t('socialnetwork.vocab.courses.exerciseExamFailedQuestionLabel') }} {{ index + 1 }}:</strong>
+                {{ item.question }}
+              </p>
+              <p class="exam-failed-review__answer">
+                <strong>{{ $t('socialnetwork.vocab.courses.exerciseExamFailedYourAnswerLabel') }}:</strong>
+                {{ item.userAnswer || $t('socialnetwork.vocab.courses.exerciseExamFailedNoAnswer') }}
+              </p>
+              <p class="exam-failed-review__answer">
+                <strong>{{ $t('socialnetwork.vocab.courses.correctAnswer') }}:</strong>
+                {{ item.correctAnswer || '—' }}
+              </p>
+            </li>
+          </ul>
+        </div>
       </div>
       <div class="dialog-footer">
         <button type="button" class="dialog-button dialog-button--primary" @click="closeChapterExamFailedDialog">
@@ -1053,6 +1072,7 @@ export default {
       exerciseReinforcementMessage: '',
       showChapterExamFailedDialog: false,
       chapterExamFailedScore: 0,
+      chapterExamFailedDetails: [],
       /** Index in scrambledChapterExamExercises bei Ein-Frage-Ansicht */
       exerciseSequentialIndex: 0,
       /** Aus vorherigen Lektionen (MC-Optionen nach Fragentyp Ziel-/Muttersprache) */
@@ -2049,6 +2069,42 @@ export default {
     closeChapterExamFailedDialog() {
       this.showChapterExamFailedDialog = false;
     },
+    formatExerciseAnswerForReview(exercise, rawAnswer) {
+      if (rawAnswer === null || rawAnswer === undefined) return '';
+      const type = this.getExerciseType(exercise);
+      if (type === 'multiple_choice') {
+        const options = this.getOptions(exercise);
+        const idx = Number(rawAnswer);
+        if (Number.isInteger(idx) && idx >= 0 && idx < options.length) {
+          return String(options[idx] ?? '');
+        }
+      }
+      if (Array.isArray(rawAnswer)) {
+        return rawAnswer
+          .map((v) => String(v || '').trim())
+          .filter(Boolean)
+          .join(' | ');
+      }
+      return String(rawAnswer || '').trim();
+    },
+    buildChapterExamFailedDetails() {
+      const all = this.effectiveExercises;
+      if (!Array.isArray(all) || all.length === 0) return [];
+      const out = [];
+      all.forEach((exercise) => {
+        const result = this.exerciseResults[exercise.id];
+        if (!result || result.correct) return;
+        const question = String(this.getQuestionText(exercise) || exercise.title || '').trim();
+        const userAnswerRaw = this.exerciseAnswers[exercise.id];
+        out.push({
+          id: exercise.id,
+          question,
+          userAnswer: this.formatExerciseAnswerForReview(exercise, userAnswerRaw),
+          correctAnswer: String(result.correctAnswer || '').trim()
+        });
+      });
+      return out;
+    },
     clearChapterExamAttemptState() {
       const all = this.effectiveExercises;
       if (!all.length) return;
@@ -2064,6 +2120,7 @@ export default {
       this.buildMcRandomizedOptions();
     },
     handleChapterExamFailed(score) {
+      this.chapterExamFailedDetails = this.buildChapterExamFailedDetails();
       this.exerciseRetryPending = true;
       this.exerciseRetryPendingSinceAttempts = this.vocabTrainerTotalAttempts;
       this.clearChapterExamAttemptState();
@@ -4234,6 +4291,31 @@ export default {
   font-weight: 700;
 }
 
+.exam-failed-review {
+  margin-top: 14px;
+  padding-top: 12px;
+  border-top: 1px solid rgba(133, 100, 4, 0.28);
+}
+
+.exam-failed-review h4 {
+  margin: 0 0 8px;
+  font-size: 0.98rem;
+}
+
+.exam-failed-review ul {
+  margin: 0;
+  padding-left: 18px;
+}
+
+.exam-failed-review li {
+  margin-bottom: 10px;
+}
+
+.exam-failed-review__question,
+.exam-failed-review__answer {
+  margin: 0 0 4px;
+}
+
 .exercise-flow-header {
   display: flex;
   justify-content: space-between;