feat(backend): #359 1단계 — google_place_id 중복 조회 API

- GET /api/admin/restaurants/duplicates/place-id (어드민 전용)
- 그룹별 식당 목록 + video/review/memo 카운트 동봉
- Mapper: findDuplicatePlaceIdRows + Service 그룹핑
- 정리/병합 + UNIQUE 제약은 데이터 위험 분리 위해 후속 PR로

Refs: #359 (조회 단계 완료)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend-java/src/main/resources/mybatis/mapper/RestaurantMapper.xml

@@ -353,4 +353,21 @@
         SELECT COUNT(*) FROM video_restaurants WHERE relevance_evaluated_at IS NULL
     </select>
 
+    <!-- #359 1단계 — google_place_id 중복 조회 (그룹 식당 + 참조 카운트) -->
+    <select id="findDuplicatePlaceIdRows" resultType="map">
+        SELECT r.id, r.google_place_id, r.name, r.address,
+               TO_CHAR(r.created_at, 'YYYY-MM-DD"T"HH24:MI:SS') AS created_at,
+               r.hidden,
+               (SELECT COUNT(*) FROM video_restaurants vr WHERE vr.restaurant_id = r.id) AS video_count,
+               (SELECT COUNT(*) FROM user_reviews rv WHERE rv.restaurant_id = r.id) AS review_count,
+               (SELECT COUNT(*) FROM user_memos mm WHERE mm.restaurant_id = r.id) AS memo_count
+        FROM restaurants r
+        WHERE r.google_place_id IN (
+            SELECT google_place_id FROM restaurants
+            WHERE google_place_id IS NOT NULL
+            GROUP BY google_place_id HAVING COUNT(*) > 1
+        )
+        ORDER BY r.google_place_id, r.created_at
+    </select>
+
 </mapper>