feat: 분류 순서변경(reorder) + 월 예상 수입 설정 API

- 분류: sort_order reorder 엔드포인트, 생성 시 맨 뒤 배치
- 예산: account_setting 테이블 + 월 예상 수입 GET/PUT

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

src/main/java/com/sb/web/account/service/AccountSettingService.java

@@ -0,0 +1,25 @@
+package com.sb.web.account.service;
+
+import com.sb.web.account.mapper.AccountSettingMapper;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+/**
+ * 사용자별 가계부 설정 서비스 (월 예상 수입 등).
+ */
+@Service
+@RequiredArgsConstructor
+public class AccountSettingService {
+
+    private final AccountSettingMapper settingMapper;
+
+    public Long getExpectedIncome(Long memberId) {
+        return settingMapper.findExpectedIncome(memberId);
+    }
+
+    @Transactional
+    public void setExpectedIncome(Long memberId, Long expectedIncome) {
+        settingMapper.upsertExpectedIncome(memberId, expectedIncome);
+    }
+}

src/main/java/com/sb/web/account/service/CategoryService.java

@@ -35,12 +35,27 @@ public class CategoryService {
         if (categoryMapper.countByName(memberId, req.getType(), name, null) > 0) {
             throw new ApiException(HttpStatus.CONFLICT, "이미 존재하는 분류입니다.");
         }
+        Integer max = categoryMapper.maxSortOrder(memberId, req.getType());
+        int order = (max == null ? 0 : max + 1);
         AccountCategory c = AccountCategory.builder()
-                .memberId(memberId).type(req.getType()).name(name).sortOrder(0).build();
+                .memberId(memberId).type(req.getType()).name(name).sortOrder(order).build();
         categoryMapper.insert(c);
         return CategoryResponse.from(c);
     }
 
+    /** 드래그앤드랍 순서 변경: 전달된 id 순서대로 sort_order 재설정 (본인·동일 타입만) */
+    @Transactional
+    public List<CategoryResponse> reorder(Long memberId, String type, List<Long> ids) {
+        int i = 0;
+        for (Long id : ids) {
+            AccountCategory c = categoryMapper.findByIdAndMember(id, memberId);
+            if (c != null && c.getType().equals(type)) {
+                categoryMapper.updateSortOrder(id, memberId, i++);
+            }
+        }
+        return list(memberId);
+    }
+
     /** 이름만 변경 가능. 변경 시 기존 내역·예산의 분류명도 함께 갱신 */
     @Transactional
     public CategoryResponse update(Long id, CategoryRequest req, Long memberId) {