[Refactor] 카테고리 계층별 조회 구현

src/main/java/com/irum/come2us/domain/category/application/service/CategoryService.java

@@ -22,10 +22,17 @@ public class CategoryService {
 
     // ------------------- 전체 조회 -------------------
     @Transactional(readOnly = true)
-    public List<CategoryResponse> findAllCategories() {
-        return categoryRepository.findAll().stream()
+    public List<CategoryResponse> findRootCategories() {
+        return categoryRepository.findByParentIsNull().stream()
                 .map(CategoryResponse::fromEntity)
-                .collect(Collectors.toList());
+                .toList();
+    }
+
+    @Transactional(readOnly = true)
+    public List<CategoryResponse> findByParentId(UUID parentId) {
+        return categoryRepository.findChildrenByParentId(parentId).stream()
+                .map(CategoryResponse::fromEntity)
+                .toList();
     }
 
     // ------------------- 단일 조회 -------------------

src/main/java/com/irum/come2us/domain/category/domain/entity/Category.java

@@ -1,5 +1,6 @@
 package com.irum.come2us.domain.category.domain.entity;
 
+import com.irum.come2us.global.domain.BaseEntity;
 import com.irum.come2us.global.presentation.advice.exception.CommonException;
 import com.irum.come2us.global.presentation.advice.exception.errorcode.CategoryErrorCode;
 import jakarta.persistence.*;
@@ -15,7 +16,7 @@
 @NoArgsConstructor(access = AccessLevel.PROTECTED)
 @AllArgsConstructor(access = AccessLevel.PRIVATE)
 @Builder(access = AccessLevel.PRIVATE)
-public class Category {
+public class Category extends BaseEntity {
 
     private static final int MAX_DEPTH = 3;
 

src/main/java/com/irum/come2us/domain/category/presentation/controller/CategoryController.java

@@ -18,8 +18,11 @@ public class CategoryController {
 
     // ------------------- 전체 조회 -------------------
     @GetMapping
-    public List<CategoryResponse> getAllCategories() {
-        return categoryService.findAllCategories();
+    public List<CategoryResponse> getAllCategories(@RequestParam(required = false) UUID parentId) {
+        if (parentId != null) {
+            return categoryService.findByParentId(parentId);
+        }
+        return categoryService.findRootCategories();
     }
 
     // ------------------- 단일 조회 -------------------