feat: 분류 대/소분류(2단계) — account_category.parent_id

- parent_id 추가(CREATE + ALTER IF NOT EXISTS 멱등 마이그레이션)
- 도메인/DTO/매퍼에 parentId 노출, 2단계 검증(대분류 아래만 소분류)
- 자식 있는 대분류는 소분류화·삭제 차단(countChildren)
- 통계/예산/내역은 소분류 이름 기준 그대로(무변경)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/resources/mapper/CategoryMapper.xml

@@ -8,23 +8,29 @@
         <result property="memberId" column="member_id"/>
         <result property="type" column="type"/>
         <result property="name" column="name"/>
+        <result property="parentId" column="parent_id"/>
         <result property="sortOrder" column="sort_order"/>
         <result property="createdAt" column="created_at"/>
     </resultMap>
 
     <select id="findByMember" parameterType="long" resultMap="categoryResultMap">
-        SELECT id, member_id, type, name, sort_order, created_at
+        SELECT id, member_id, type, name, parent_id, sort_order, created_at
         FROM account_category
         WHERE member_id = #{memberId}
         ORDER BY type, sort_order, name
     </select>
 
     <select id="findByIdAndMember" resultMap="categoryResultMap">
-        SELECT id, member_id, type, name, sort_order, created_at
+        SELECT id, member_id, type, name, parent_id, sort_order, created_at
         FROM account_category
         WHERE id = #{id} AND member_id = #{memberId}
     </select>
 
+    <select id="countChildren" resultType="int">
+        SELECT COUNT(*) FROM account_category
+        WHERE member_id = #{memberId} AND parent_id = #{parentId}
+    </select>
+
     <select id="countByName" resultType="int">
         SELECT COUNT(*) FROM account_category
         WHERE member_id = #{memberId} AND type = #{type} AND name = #{name}
@@ -33,17 +39,17 @@
 
     <insert id="insert" parameterType="com.sb.web.account.domain.AccountCategory"
             useGeneratedKeys="true" keyProperty="id">
-        INSERT INTO account_category (member_id, type, name, sort_order, created_at)
-        VALUES (#{memberId}, #{type}, #{name}, #{sortOrder}, NOW())
+        INSERT INTO account_category (member_id, type, name, parent_id, sort_order, created_at)
+        VALUES (#{memberId}, #{type}, #{name}, #{parentId}, #{sortOrder}, NOW())
     </insert>
 
     <insert id="insertIgnore" parameterType="com.sb.web.account.domain.AccountCategory">
-        INSERT IGNORE INTO account_category (member_id, type, name, sort_order, created_at)
-        VALUES (#{memberId}, #{type}, #{name}, 0, NOW())
+        INSERT IGNORE INTO account_category (member_id, type, name, parent_id, sort_order, created_at)
+        VALUES (#{memberId}, #{type}, #{name}, #{parentId}, 0, NOW())
     </insert>
 
     <update id="update" parameterType="com.sb.web.account.domain.AccountCategory">
-        UPDATE account_category SET name = #{name}
+        UPDATE account_category SET name = #{name}, parent_id = #{parentId}
         WHERE id = #{id} AND member_id = #{memberId}
     </update>