feat(exercises): enhance context in gap fill exercises and update migration for route descriptions

backend/migrations-active/20260902000000-repair-bisaya-directions-context-gap.cjs

@@ -0,0 +1,29 @@
+'use strict';
+
+/**
+ * The generated exercise for "Wege & Verkehr" used a bare `{gap}` while its
+ * instruction asked for a route description.  A gap must be embedded in the
+ * route so the learner can infer the expected direction from the context.
+ */
+module.exports = {
+  async up(queryInterface) {
+    await queryInterface.sequelize.query(`
+      UPDATE community.vocab_grammar_exercise AS exercise
+      SET title = 'Wege & Verkehr: Satz im Kontext ergänzen',
+          question_data = '{"type":"gap_fill","text":"{gap}. Tuo. Wala. Duol ra.","gaps":1}'::jsonb,
+          answer_data = '{"type":"gap_fill","answers":["Diretso"]}'::jsonb,
+          explanation = 'Die vollständige Wegbeschreibung lautet: "Diretso. Tuo. Wala. Duol ra."'
+      FROM community.vocab_course_lesson AS lesson
+      WHERE exercise.lesson_id = lesson.id
+        AND (lesson.id = 1532 OR (lesson.course_id = 1 AND lesson.lesson_number = 55))
+        AND lesson.title = 'Wege & Verkehr'
+        AND exercise.question_data->>'type' = 'gap_fill'
+        AND exercise.question_data->>'text' = '{gap}'
+        AND exercise.answer_data->'answers' @> '["tuo"]'::jsonb;
+    `);
+  },
+
+  async down() {
+    // Do not restore the context-free task.
+  }
+};