chore: relocate backend into apps/api ahead of monorepo merge

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/database/migrations/20270101000016-create-lesson-objectives.js

@@ -0,0 +1,21 @@
+'use strict';
+
+module.exports = {
+  async up(queryInterface, Sequelize) {
+    await queryInterface.createTable('lesson_objectives', {
+      objective_id: { type: Sequelize.BIGINT, primaryKey: true, autoIncrement: true },
+      lesson_id:    { type: Sequelize.BIGINT, allowNull: false, references: { model: 'lessons', key: 'lesson_id' }, onDelete: 'CASCADE' },
+      text:         { type: Sequelize.TEXT, allowNull: false },
+      order_index:  { type: Sequelize.INTEGER, defaultValue: 0 },
+      createdAt:    { type: Sequelize.DATE, allowNull: false },
+      updatedAt:    { type: Sequelize.DATE, allowNull: false },
+      deletedAt:    { type: Sequelize.DATE, allowNull: true },
+    });
+
+    await queryInterface.addIndex('lesson_objectives', ['lesson_id']);
+  },
+
+  async down(queryInterface) {
+    await queryInterface.dropTable('lesson_objectives');
+  },
+};