feat: add A2-B1 course expansion features including listening activities and conversation sessions

- Updated VocabCourseView.vue to display CEFR level for courses.
- Enhanced VocabLessonView.vue with new sections for listening activities and conversation labs, including audio controls and transcript toggling.
- Created migration to add new columns to vocab_course and new tables for conversation sessions and listening activities.
- Implemented models for vocab_conversation_session and vocab_listening_activity.
- Developed scripts to create new A2 and B1 bridge courses with structured lesson plans.
- Documented the A2-B1 expansion plan detailing course structure, learning goals, and assessment criteria.

backend/migrations-active/20260827000000-add-vocab-a2-learning-features.cjs

@@ -0,0 +1,54 @@
+'use strict';
+
+module.exports = {
+  async up(queryInterface) {
+    await queryInterface.sequelize.transaction(async (transaction) => {
+      await queryInterface.sequelize.query(`
+        ALTER TABLE community.vocab_course
+          ADD COLUMN IF NOT EXISTS cefr_level TEXT,
+          ADD COLUMN IF NOT EXISTS course_kind TEXT NOT NULL DEFAULT 'core',
+          ADD COLUMN IF NOT EXISTS prerequisite_course_id INTEGER NULL
+            REFERENCES community.vocab_course(id) ON DELETE SET NULL;
+
+        CREATE TABLE IF NOT EXISTS community.vocab_conversation_session (
+          id SERIAL PRIMARY KEY,
+          user_id INTEGER NOT NULL REFERENCES community."user"(id) ON DELETE CASCADE,
+          lesson_id INTEGER NOT NULL REFERENCES community.vocab_course_lesson(id) ON DELETE CASCADE,
+          scenario JSONB NOT NULL DEFAULT '{}'::jsonb,
+          turns JSONB NOT NULL DEFAULT '[]'::jsonb,
+          summary JSONB NULL,
+          status TEXT NOT NULL DEFAULT 'active',
+          created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+          updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+        );
+        CREATE INDEX IF NOT EXISTS vocab_conversation_session_user_lesson_idx
+          ON community.vocab_conversation_session(user_id, lesson_id, updated_at DESC);
+
+        CREATE TABLE IF NOT EXISTS community.vocab_listening_activity (
+          id SERIAL PRIMARY KEY,
+          lesson_id INTEGER NOT NULL REFERENCES community.vocab_course_lesson(id) ON DELETE CASCADE,
+          audio_url TEXT NOT NULL,
+          transcript TEXT NOT NULL,
+          translation TEXT NULL,
+          speaker_profile JSONB NOT NULL DEFAULT '{}'::jsonb,
+          speed TEXT NOT NULL DEFAULT 'natural',
+          questions JSONB NOT NULL DEFAULT '[]'::jsonb,
+          created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+        );
+        CREATE INDEX IF NOT EXISTS vocab_listening_activity_lesson_idx
+          ON community.vocab_listening_activity(lesson_id);
+      `, { transaction });
+    });
+  },
+
+  async down(queryInterface) {
+    await queryInterface.sequelize.query(`
+      DROP TABLE IF EXISTS community.vocab_listening_activity;
+      DROP TABLE IF EXISTS community.vocab_conversation_session;
+      ALTER TABLE community.vocab_course
+        DROP COLUMN IF EXISTS prerequisite_course_id,
+        DROP COLUMN IF EXISTS course_kind,
+        DROP COLUMN IF EXISTS cefr_level;
+    `);
+  }
+};

backend/migrations-active/20260827000001-fix-bisaya-lesson-46-context-gap.cjs

@@ -0,0 +1,22 @@
+'use strict';
+
+/** Repairs the already generated exercise that rendered as a bare blank. */
+module.exports = {
+  async up(queryInterface) {
+    await queryInterface.sequelize.query(`
+      UPDATE community.vocab_grammar_exercise AS exercise
+      SET question_data = '{"type":"gap_fill","text":"{gap} ka padulong?","gaps":1}'::jsonb,
+          answer_data = '{"type":"gap_fill","answers":["Asa"]}'::jsonb,
+          explanation = 'Das Kernmuster lautet: "Asa ka padulong?"'
+      FROM community.vocab_course_lesson AS lesson
+      WHERE exercise.lesson_id = lesson.id
+        AND lesson.lesson_number = 46
+        AND lesson.title = 'Fragen im Alltag vertiefen'
+        AND exercise.title = 'Fragen im Alltag vertiefen: Kernmuster ergänzen'
+        AND exercise.question_data->>'text' = '{gap}';
+    `);
+  },
+  async down() {
+    // The old exercise has no useful learner-visible prompt and is not restored.
+  }
+};