feat(vocab): implement repeat queue management in VocabService and VocabLessonView

- Added a new method in VocabService to sanitize and manage a repeat queue for vocabulary items, enhancing the learning process.
- Updated VocabLessonView to incorporate repeat queue functionality, allowing for better tracking of vocabulary that needs review.
- Refactored existing logic to ensure seamless integration of repeat queue features, improving user experience during vocabulary lessons.

backend/services/vocabService.js

@@ -115,6 +115,21 @@ export default class VocabService {
     return sanitized;
   }
 
+  _sanitizeRepeatQueue(value) {
+    if (!Array.isArray(value)) {
+      return [];
+    }
+
+    return value
+      .slice(0, 100)
+      .map((entry) => ({
+        key: this._sanitizeShortString(entry?.key, 200),
+        dueAfter: this._clampInteger(entry?.dueAfter, { min: 0, max: 50 }),
+        stageIndex: this._clampInteger(entry?.stageIndex, { min: 0, max: 10 })
+      }))
+      .filter((entry) => entry.key);
+  }
+
   _sanitizeLessonState(value) {
     if (!value || typeof value !== 'object' || Array.isArray(value)) {
       return {};
@@ -136,6 +151,7 @@ export default class VocabService {
       'vocabTrainerCurrentAttempts',
       'vocabTrainerReviewAttempts',
       'vocabTrainerStats',
+      'vocabTrainerRepeatQueue',
       'exerciseAnswers',
       'exerciseResults',
       'exerciseRetryPending',
@@ -165,6 +181,7 @@ export default class VocabService {
       vocabTrainerCurrentAttempts: this._clampInteger(value.vocabTrainerCurrentAttempts, { max: 10000 }),
       vocabTrainerReviewAttempts: this._clampInteger(value.vocabTrainerReviewAttempts, { max: 10000 }),
       vocabTrainerStats: this._sanitizeVocabTrainerStats(value.vocabTrainerStats),
+      vocabTrainerRepeatQueue: this._sanitizeRepeatQueue(value.vocabTrainerRepeatQueue),
       exerciseAnswers: this._sanitizeExerciseAnswers(value.exerciseAnswers),
       exerciseResults: this._sanitizeExerciseResults(value.exerciseResults),
       exerciseRetryPending: Boolean(value.exerciseRetryPending),