fix(study): quiz_session 결과 — StudyQuestionImage.position → sort_order 재사용

PR-10 결과 페이지에서 GET /quiz-sessions/{sid} 가 500. 이미지 batch 호출에서
존재하지 않는 컬럼 position 사용 → AttributeError. 기존
_images_for_questions_batch 헬퍼 (sort_order 기준 + served_url 포함) 재사용.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/api/study_topics.py

@@ -1538,21 +1538,12 @@ async def get_quiz_session(
         ).scalars().all()
         by_id = {q.id: q for q in rows}
 
-        # 이미지 batch
-        img_rows = (
-            await session.execute(
-                select(StudyQuestionImage)
-                .where(StudyQuestionImage.study_question_id.in_(qids))
-                .order_by(StudyQuestionImage.study_question_id, StudyQuestionImage.position)
-            )
-        ).scalars().all()
-        images_map: dict[int, list[dict]] = {}
-        for im in img_rows:
-            images_map.setdefault(im.study_question_id, []).append({
-                "id": im.id,
-                "served_url": f"/api/study-questions/{im.study_question_id}/images/{im.id}",
-                "position": im.position,
-            })
+        # 이미지 batch — 기존 study_questions._images_for_questions_batch 재사용 (sort_order 기준).
+        from api.study_questions import _images_for_questions_batch
+        images_typed = await _images_for_questions_batch(session, qids)
+        images_map: dict[int, list[dict]] = {
+            qid: [it.model_dump() for it in items] for qid, items in images_typed.items()
+        }
 
         # attempt count batch (per question)
         stat_rows = (