feat(account): 대출 계좌 loan_amount/loan_rate/loan_method/loan_months/loan_start 필드 추가

- wallet 테이블: loan_amount(실행금액), loan_rate(연이자율%), loan_method(상환방식),
  loan_months(기간), loan_start(시작일) ALTER TABLE 추가
- Wallet 도메인/DTO/Mapper/Service 동기화
- WalletResponse.from()에 대출 필드 반영

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

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

@@ -535,6 +535,12 @@ public class AccountService {
         wallet.setOpeningBalance(req.getOpeningBalance() != null ? req.getOpeningBalance() : 0L);
         wallet.setOpeningDate(req.getOpeningDate());
         wallet.setCurrentValue("INVEST".equals(req.getType()) ? req.getCurrentValue() : null);
+        boolean isLoan = "LOAN".equals(req.getType());
+        wallet.setLoanAmount(isLoan ? req.getLoanAmount() : null);
+        wallet.setLoanRate(isLoan ? req.getLoanRate() : null);
+        wallet.setLoanMethod(isLoan ? blankToNull(req.getLoanMethod()) : null);
+        wallet.setLoanMonths(isLoan ? req.getLoanMonths() : null);
+        wallet.setLoanStart(isLoan ? req.getLoanStart() : null);
         walletMapper.update(wallet);
         return WalletResponse.from(wallet, balanceMap(memberId).getOrDefault(id, wallet.getOpeningBalance()));
     }
@@ -564,6 +570,7 @@ public class AccountService {
     }
 
     private Wallet toWallet(WalletRequest req) {
+        boolean isLoan = "LOAN".equals(req.getType());
         return Wallet.builder()
                 .type(req.getType())
                 .name(req.getName().trim())
@@ -573,6 +580,11 @@ public class AccountService {
                 .openingBalance(req.getOpeningBalance() != null ? req.getOpeningBalance() : 0L)
                 .openingDate(req.getOpeningDate())
                 .currentValue("INVEST".equals(req.getType()) ? req.getCurrentValue() : null)
+                .loanAmount(isLoan ? req.getLoanAmount() : null)
+                .loanRate(isLoan ? req.getLoanRate() : null)
+                .loanMethod(isLoan ? blankToNull(req.getLoanMethod()) : null)
+                .loanMonths(isLoan ? req.getLoanMonths() : null)
+                .loanStart(isLoan ? req.getLoanStart() : null)
                 .build();
     }