Implement vocab course and grammar exercise features in backend and frontend

- Added new course management functionalities in VocabController, including creating, updating, and deleting courses and lessons.
- Implemented enrollment and progress tracking for courses, along with grammar exercise creation and management.
- Updated database schema to include tables for courses, lessons, enrollments, and grammar exercises.
- Enhanced frontend with new routes and views for course listing and details, including internationalization support for course-related texts.
- Improved user experience by adding navigation to courses from the main vocab trainer view.

backend/migrations/20260115000003-add-course-learning-goals.cjs

@@ -0,0 +1,33 @@
+/* eslint-disable */
+'use strict';
+
+module.exports = {
+  async up(queryInterface) {
+    // Lernziele für Lektionen
+    await queryInterface.sequelize.query(`
+      ALTER TABLE community.vocab_course_lesson
+      ADD COLUMN IF NOT EXISTS target_minutes INTEGER,
+      ADD COLUMN IF NOT EXISTS target_score_percent INTEGER DEFAULT 80,
+      ADD COLUMN IF NOT EXISTS requires_review BOOLEAN DEFAULT false;
+    `);
+
+    // Kommentare hinzufügen
+    await queryInterface.sequelize.query(`
+      COMMENT ON COLUMN community.vocab_course_lesson.target_minutes IS 
+        'Zielzeit in Minuten für diese Lektion';
+      COMMENT ON COLUMN community.vocab_course_lesson.target_score_percent IS 
+        'Mindestpunktzahl in Prozent zum Abschluss (z.B. 80)';
+      COMMENT ON COLUMN community.vocab_course_lesson.requires_review IS 
+        'Muss diese Lektion wiederholt werden, wenn Ziel nicht erreicht?';
+    `);
+  },
+
+  async down(queryInterface) {
+    await queryInterface.sequelize.query(`
+      ALTER TABLE community.vocab_course_lesson
+      DROP COLUMN IF EXISTS target_minutes,
+      DROP COLUMN IF EXISTS target_score_percent,
+      DROP COLUMN IF EXISTS requires_review;
+    `);
+  }
+};