feat: 월별 예산 + 전월/다음달 복사

- budget 테이블에 year/month 추가, (member,category)→(member,category,year,month) 유니크 교체
  기존 상시 예산은 현재 월로 1회 이관
- 예산 조회/생성/현황/기간차트를 월별로(findByMember에 year/month)
- copyMonth: 다른 월 예산을 대상 월로 복사(같은 분류 덮어씀) + POST /budgets/copy
- 백업 복구 시 예산은 현재 월로 등록

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

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

@@ -156,11 +156,12 @@ public class BackupService {
             }
         }
 
-        // 7) 예산
+        // 7) 예산 — 복구 시 현재 월 예산으로 등록(백업엔 월 정보 없음)
         if (req.getBudgets() != null) {
+            java.time.LocalDate today = java.time.LocalDate.now();
             for (BudgetRequest b : req.getBudgets()) {
                 if (b == null || b.getCategory() == null) continue;
-                budgetService.create(b, memberId);
+                budgetService.create(b, memberId, today.getYear(), today.getMonthValue());
             }
         }
 

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

@@ -31,36 +31,46 @@ public class BudgetService {
     private final BudgetMapper budgetMapper;
     private final AccountEntryMapper entryMapper;
 
-    public List<BudgetResponse> list(Long memberId) {
-        return budgetMapper.findByMember(memberId).stream().map(BudgetResponse::from).toList();
+    public List<BudgetResponse> list(Long memberId, int year, int month) {
+        return budgetMapper.findByMember(memberId, year, month).stream().map(BudgetResponse::from).toList();
     }
 
     @Transactional
-    public BudgetResponse create(BudgetRequest req, Long memberId) {
+    public BudgetResponse create(BudgetRequest req, Long memberId, int year, int month) {
         String category = req.getCategory().trim();
-        if (budgetMapper.countByCategory(memberId, category, null) > 0) {
+        if (budgetMapper.countByCategory(memberId, category, null, year, month) > 0) {
             throw new ApiException(HttpStatus.CONFLICT, "이미 예산이 설정된 카테고리입니다.");
         }
         Budget budget = toBudget(req, category);
         budget.setMemberId(memberId);
+        budget.setYear(year);
+        budget.setMonth(month);
         budgetMapper.insert(budget);
         return BudgetResponse.from(budget);
     }
 
     @Transactional
     public BudgetResponse update(Long id, BudgetRequest req, Long memberId) {
-        mustFind(id, memberId);
+        Budget existing = mustFind(id, memberId);
         String category = req.getCategory().trim();
-        if (budgetMapper.countByCategory(memberId, category, id) > 0) {
+        if (budgetMapper.countByCategory(memberId, category, id, existing.getYear(), existing.getMonth()) > 0) {
             throw new ApiException(HttpStatus.CONFLICT, "이미 예산이 설정된 카테고리입니다.");
         }
         Budget budget = toBudget(req, category);
         budget.setId(id);
         budget.setMemberId(memberId);
+        budget.setYear(existing.getYear());
+        budget.setMonth(existing.getMonth());
         budgetMapper.update(budget);
         return BudgetResponse.from(budget);
     }
 
+    /** fromYear/fromMonth 예산을 toYear/toMonth 로 복사(같은 분류 덮어씀). 복사된 건수 반환 */
+    @Transactional
+    public int copy(Long memberId, int fromYear, int fromMonth, int toYear, int toMonth) {
+        return budgetMapper.copyMonth(memberId, fromYear, fromMonth, toYear, toMonth);
+    }
+
     @Transactional
     public void delete(Long id, Long memberId) {
         mustFind(id, memberId);
@@ -79,7 +89,7 @@ public class BudgetService {
         }
 
         List<BudgetStatus> result = new ArrayList<>();
-        for (Budget b : budgetMapper.findByMember(memberId)) {
+        for (Budget b : budgetMapper.findByMember(memberId, year, month)) {
             long monthlyBudget = monthlyBudget(b, daysInMonth);
             long spent = spentByCategory.getOrDefault(b.getCategory(), 0L);
             result.add(BudgetStatus.builder()
@@ -103,7 +113,8 @@ public class BudgetService {
         int y = year != null ? year : Year.now().getValue();
         int m = month != null ? month : 1;
 
-        List<Budget> budgets = budgetMapper.findByMember(memberId);
+        // 기간 차트는 선택 월의 예산을 기준으로 각 버킷에 적용(월별 예산 도입 전 동작과 동일)
+        List<Budget> budgets = budgetMapper.findByMember(memberId, y, m);
         Map<String, Long> expense = new HashMap<>();
         for (Map<String, Object> row : entryMapper.statsByPeriod(memberId, unit, year, month)) {
             expense.put(String.valueOf(((Number) row.get("bucket")).longValue()),