feat(vocab): implement SRS features and enhance vocabulary management

- Added new endpoints in vocabController for retrieving SRS due items and reviewing SRS items, improving spaced repetition support.
- Updated vocabService to handle SRS item creation and scheduling, ensuring effective tracking of vocabulary exposure.
- Enhanced vocabRouter with new routes for SRS functionalities, facilitating user interaction with spaced repetition features.
- Modified VocabPracticeDialog and VocabCourseView to integrate SRS due items, providing users with timely review opportunities.
- Updated translations and UI elements to reflect new SRS features, enhancing user experience and accessibility.

backend/models/index.js

@@ -156,6 +156,7 @@ import VocabCourseProgress from './community/vocab_course_progress.js';
 import VocabGrammarExerciseType from './community/vocab_grammar_exercise_type.js';
 import VocabGrammarExercise from './community/vocab_grammar_exercise.js';
 import VocabGrammarExerciseProgress from './community/vocab_grammar_exercise_progress.js';
+import VocabSrsItem from './community/vocab_srs_item.js';
 import CalendarEvent from './community/calendar_event.js';
 
 const models = {
@@ -318,6 +319,7 @@ const models = {
   VocabGrammarExerciseType,
   VocabGrammarExercise,
   VocabGrammarExerciseProgress,
+  VocabSrsItem,
   
   // Calendar
   CalendarEvent,