refactor: InflowGroupBucketService 리플렉션 제거

Field 리플렉션으로 groupBucketList에 직접 접근하던 getCustomGroupBucket()을
InflowControlManager.getGroupBucket() public 메서드 호출로 교체.
불필요한 java.lang.reflect.Field, Map import 및 @SuppressWarnings 제거.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/java/com/eactive/eai/manage/inflow/InflowGroupBucketService.java

@@ -1,9 +1,7 @@
 package com.eactive.eai.manage.inflow;
 
-import java.lang.reflect.Field;
 import java.util.ArrayList;
 import java.util.List;
-import java.util.Map;
 
 import org.springframework.stereotype.Service;
 
@@ -72,21 +70,8 @@ public class InflowGroupBucketService {
         return dto;
     }
 
-    /**
-     * 그룹 버킷 조회 (리플렉션 사용)
-     */
     public CustomGroupBucket getCustomGroupBucket(String groupId) {
-        try {
-            InflowControlManager manager = InflowControlManager.getInstance();
-            Field field = InflowControlManager.class.getDeclaredField("groupBucketList");
-            field.setAccessible(true);
-            @SuppressWarnings("unchecked")
-            Map<String, CustomGroupBucket> groupBucketList =
-                (Map<String, CustomGroupBucket>) field.get(manager);
-            return groupBucketList.get(groupId);
-        } catch (Exception e) {
-            return null;
-        }
+        return InflowControlManager.getInstance().getGroupBucket(groupId);
     }
 
     public List<GroupBucketStatusDTO> getAllGroupBucketStatus() {