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

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

apps/api/utils/courses/grading.util.js

@@ -0,0 +1,57 @@
+"use strict";
+
+/**
+ * Grades a submission against the stored correct answers.
+ *
+ * The breakdown returned here is what gets sent back to the client, so it
+ * deliberately never includes which option(s) were correct — only whether
+ * the user's own answer for each question was right or wrong. Explanation
+ * text is included only when the question was answered correctly, since
+ * showing it for a wrong answer would effectively reveal the correct one.
+ *
+ * @param {Array}  questions - QuizQuestion rows w/ .options (incl. is_correct), already fetched
+ * @param {Object} answers   - { [question_id]: optionId | optionId[] } submitted by the client
+ */
+function gradeSubmission(questions, answers = {}) {
+  let totalPoints = 0;
+  let earnedPoints = 0;
+
+  const breakdown = questions.map((q) => {
+    const points = q.points ?? 1;
+    totalPoints += points;
+
+    const correctIds = (q.options ?? [])
+      .filter((o) => o.is_correct)
+      .map((o) => o.option_id);
+
+    const submitted = answers[q.question_id];
+    const submittedIds = Array.isArray(submitted)
+      ? submitted
+      : (submitted !== undefined && submitted !== null ? [submitted] : []);
+
+    const isCorrect =
+      submittedIds.length === correctIds.length &&
+      correctIds.every((id) => submittedIds.includes(id));
+
+    if (isCorrect) earnedPoints += points;
+
+    return {
+      question_id: q.question_id,
+      type: q.type,
+      question: q.question,
+      points,
+      is_correct: isCorrect,
+      selected_option_ids: submittedIds,
+      explanation: isCorrect ? (q.explanation ?? null) : null,
+      options: (q.options ?? []).map((o) => ({
+        option_id: o.option_id,
+        text: o.text,
+      })),
+    };
+  });
+
+  const score = totalPoints > 0 ? Math.round((earnedPoints / totalPoints) * 100) : 0;
+  return { totalPoints, earnedPoints, score, breakdown };
+}
+
+module.exports = { gradeSubmission };