feat(bisaya): update prompts and add migration for food context gap exercise

backend/migrations-active/20260904000000-repair-bisaya-food-context-gap.cjs

@@ -0,0 +1,25 @@
+'use strict';
+
+/** Replaces a context-free food gap with a clearly answerable table setting. */
+module.exports = {
+  async up(queryInterface) {
+    await queryInterface.sequelize.query(`
+      UPDATE community.vocab_grammar_exercise AS exercise
+      SET title = 'Essen & Trinken: Auf dem Tisch ergänzen',
+          instruction = 'Auf dem Tisch stehen Reis, Fisch und Wasser. Ergänze das fehlende Bisaya-Wort.',
+          question_data = '{"type":"gap_fill","text":"{gap}, isda ug tubig.","gaps":1}'::jsonb,
+          answer_data = '{"type":"gap_fill","answers":["Kan-on"]}'::jsonb,
+          explanation = 'Kan-on bedeutet gekochter Reis. Der ganze Ausdruck lautet: „Kan-on, isda ug tubig.“'
+      FROM community.vocab_course_lesson AS lesson
+      WHERE exercise.lesson_id = lesson.id
+        AND lesson.lesson_number = 8
+        AND lesson.title = 'Essen & Trinken'
+        AND exercise.exercise_number = 3
+        AND exercise.title = 'Essen & Trinken: Kernmuster ergänzen';
+    `);
+  },
+
+  async down() {
+    // Do not restore the ambiguous exercise.
+  }
+};