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

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

apps/api/models/courses/quiz_question.mdl.js

@@ -0,0 +1,28 @@
+const { DataTypes } = require("sequelize");
+const sequelize = require("../../config/db.config");
+
+const QuizQuestion = sequelize.define("QuizQuestion", {
+  question_id:  { type: DataTypes.BIGINT, primaryKey: true, autoIncrement: true },
+  uuid:         { type: DataTypes.UUID, defaultValue: DataTypes.UUIDV4, unique: true },
+
+  // polymorphic: belongs to either unit_quiz OR course_assessment
+  quiz_id:        { type: DataTypes.BIGINT, allowNull: true },   // → unit_quizzes
+  assessment_id:  { type: DataTypes.BIGINT, allowNull: true },   // → course_assessments
+
+  type: {
+    type: DataTypes.ENUM("true_false", "multiple_choice", "multi_select"),
+    allowNull: false,
+  },
+  question:    { type: DataTypes.TEXT, allowNull: false },
+  explanation: { type: DataTypes.TEXT, allowNull: true },  // shown after answer
+  order_index: { type: DataTypes.INTEGER, defaultValue: 0 },
+  points:      { type: DataTypes.INTEGER, defaultValue: 1 },
+  createdBy:   { type: DataTypes.BIGINT, allowNull: true },
+  deletedBy:   { type: DataTypes.BIGINT, allowNull: true },
+}, {
+  tableName: "quiz_questions",
+  timestamps: true,
+  paranoid: true,
+});
+
+module.exports = QuizQuestion