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/java/com/tasteby/controller/AdminRestaurantController.java

@@ -62,6 +62,15 @@ public class AdminRestaurantController {
         return Map.of("success", true, "id", id);
     }
 
+    // #359 1단계 — google_place_id 중복 조회 (정리/UNIQUE는 후속).
+    @GetMapping("/duplicates/place-id")
+    public Map<String, Object> duplicatePlaceIds() {
+        var admin = AuthUtil.requireAdmin();
+        var groups = restaurantService.findDuplicatePlaceIdGroups();
+        log.info("[ADMIN] {} duplicate place_id groups: {}", admin.getSubject(), groups.size());
+        return Map.of("groups", groups, "group_count", groups.size());
+    }
+
     /**
      * 어드민용 hidden 토글.
      */

backend-java/src/main/java/com/tasteby/mapper/RestaurantMapper.java

@@ -39,6 +39,9 @@ public interface RestaurantMapper {
 
     int countUnevaluatedLinks();
 
+    // #359 1단계 — google_place_id 중복 조회
+    List<Map<String, Object>> findDuplicatePlaceIdRows();
+
     Restaurant findById(@Param("id") String id);
 
     List<Map<String, Object>> findVideoLinks(@Param("restaurantId") String restaurantId,

backend-java/src/main/java/com/tasteby/service/RestaurantService.java

@@ -111,6 +111,23 @@ public class RestaurantService {
         return mapper.countUnevaluatedLinks();
     }
 
+    // #359 1단계 — google_place_id 중복 그룹 (참조 카운트 동봉)
+    public List<Map<String, Object>> findDuplicatePlaceIdGroups() {
+        var rows = mapper.findDuplicatePlaceIdRows().stream()
+                .map(JsonUtil::lowerKeys)
+                .toList();
+        Map<String, List<Map<String, Object>>> grouped = new LinkedHashMap<>();
+        for (var r : rows) {
+            String key = (String) r.get("google_place_id");
+            grouped.computeIfAbsent(key, k -> new ArrayList<>()).add(r);
+        }
+        List<Map<String, Object>> out = new ArrayList<>(grouped.size());
+        for (var e : grouped.entrySet()) {
+            out.add(Map.of("google_place_id", e.getKey(), "items", e.getValue()));
+        }
+        return out;
+    }
+
     public void update(String id, Map<String, Object> fields) {
         mapper.updateFields(id, fields);
     }