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/dto/WalletResponse.java

@@ -4,6 +4,7 @@ import com.sb.web.account.domain.Wallet;
 import lombok.Builder;
 import lombok.Data;
 
+import java.math.BigDecimal;
 import java.time.LocalDate;
 
 /**
@@ -31,6 +32,13 @@ public class WalletResponse {
     private Long currentValue;    // 평가액 직접입력값(퇴직연금·연금 등 수동 갱신). 있으면 총평가로 사용
     private Boolean manualValuation; // true면 평가액 직접입력형(종목 자동계산 대신)
 
+    // 대출(LOAN) 전용
+    private Long loanAmount;       // 대출 실행 금액(원금)
+    private BigDecimal loanRate;   // 연이자율(%) e.g. 5.25
+    private String loanMethod;     // EQUAL_PAYMENT / EQUAL_PRINCIPAL / BULLET
+    private Integer loanMonths;    // 대출기간(개월)
+    private LocalDate loanStart;   // 대출시작일
+
     public static WalletResponse from(Wallet w, long balance) {
         return WalletResponse.builder()
                 .id(w.getId())
@@ -43,6 +51,11 @@ public class WalletResponse {
                 .openingDate(w.getOpeningDate())
                 .balance(balance)
                 .currentValue(w.getCurrentValue())
+                .loanAmount(w.getLoanAmount())
+                .loanRate(w.getLoanRate())
+                .loanMethod(w.getLoanMethod())
+                .loanMonths(w.getLoanMonths())
+                .loanStart(w.getLoanStart())
                 .build();
     }
 }