fix(vocab): reject lexical hints paired with sentences

backend/migrations-active/20260827000000-remove-invalid-karon-srs-card.cjs

@@ -0,0 +1,17 @@
+'use strict';
+
+module.exports = {
+  async up(queryInterface) {
+    // A legacy gap-fill hint was persisted as a vocabulary answer. The pair
+    // "jetzt/heute" → "Karon naa ko diri" is not a valid translation card.
+    await queryInterface.sequelize.query(`
+      DELETE FROM community.vocab_srs_item
+      WHERE lower(trim(learning)) = 'jetzt/heute'
+        AND lower(trim(reference)) = 'karon naa ko diri';
+    `);
+  },
+
+  async down() {
+    // Do not restore an invalid study card.
+  }
+};