feat(account): 대출 실행금액 필드 추가 + 상환방식별 자동계산 분기

- loan_amount(대출 실행 금액) 컬럼 추가(DB/도메인/DTO/mapper)
- 계좌 폼: 대출 실행 금액 입력 / 기록 시작 시 잔액(기존 openingBalance) 레이블 분리
- 계좌 카드: 실행금액·금리·상환방식 표시
- 상환 자동계산 3방식 분기:
  - 원리금균등: 납입금액 입력 → 이자(잔액×월이율) / 원금(납입-이자) 분리
  - 원금균등: 실행금액÷기간=월원금, 잔액×월이율=이자 자동계산
  - 만기일시: 잔액×월이율=이자만 자동계산, 원금 0
- 자동계산 후 이자·원금 수동 조정 가능

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

src/views/account/AccountView.vue

@@ -132,23 +132,46 @@ const repayTargetLoanWallet = computed(() => {
   const w = wallets.value.find((x) => x.id === form.toWalletId)
   return w?.type === 'LOAN' && w.loanRate ? w : null
 })
-// 납입총액 입력 → 원금/이자 자동분리
+// 납입금액 입력용 (원리금균등만 사용)
 const loanPaymentAmount = ref(null)
+
+function monthlyInterestOf(loan) {
+  return Math.round(Math.abs(loan.balance || 0) * (Number(loan.loanRate) / 100 / 12))
+}
+
+// 상환방식별 자동계산: 원금균등·만기일시는 납입금액 입력 불필요
+const loanAutoResult = computed(() => {
+  const loan = repayTargetLoanWallet.value
+  if (!loan) return null
+  const interest = monthlyInterestOf(loan)
+  if (loan.loanMethod === 'BULLET') {
+    return { interest, principal: 0, total: interest, needsInput: false }
+  }
+  if (loan.loanMethod === 'EQUAL_PRINCIPAL' && loan.loanAmount && loan.loanMonths) {
+    const principal = Math.round(Number(loan.loanAmount) / loan.loanMonths)
+    return { interest, principal, total: principal + interest, needsInput: false }
+  }
+  return { interest: null, principal: null, total: null, needsInput: true }
+})
+
+watch(loanAutoResult, (r) => {
+  if (r && !r.needsInput) {
+    form.interest = r.interest
+    form.principal = r.principal
+    loanPaymentAmount.value = r.total
+  }
+})
+
 function calcLoanRepayment(payment) {
   const loan = repayTargetLoanWallet.value
   if (!loan || !payment || payment <= 0) return
-  const monthlyRate = Number(loan.loanRate) / 100 / 12
-  const remainingDebt = Math.abs(loan.balance || 0)
-  const monthlyInterest = Math.round(remainingDebt * monthlyRate)
-  if (loan.loanMethod === 'BULLET') {
-    form.interest = payment
-    form.principal = 0
-  } else {
-    form.interest = Math.min(monthlyInterest, payment)
-    form.principal = Math.max(0, payment - form.interest)
-  }
+  const interest = monthlyInterestOf(loan)
+  form.interest = Math.min(interest, payment)
+  form.principal = Math.max(0, payment - form.interest)
 }
-watch(loanPaymentAmount, (val) => { if (val) calcLoanRepayment(Number(val)) })
+watch(loanPaymentAmount, (val) => {
+  if (loanAutoResult.value?.needsInput && val) calcLoanRepayment(Number(val))
+})
 watch(() => form.toWalletId, () => {
   loanPaymentAmount.value = null
   form.principal = null
@@ -1162,15 +1185,26 @@ onMounted(async () => {
                     </option>
                   </select>
                 </label>
-                <!-- 금리 설정된 대출 계좌: 납입금액 입력 → 원금/이자 자동계산 -->
+                <!-- 금리 설정된 대출 계좌: 방식별 자동계산 -->
                 <template v-if="repayTargetLoanWallet">
-                  <label>납입금액
-                    <input v-model.number="loanPaymentAmount" type="number" min="0"
-                      placeholder="이번 달 납입할 총금액" :disabled="submitting" @input="calcLoanRepayment(loanPaymentAmount)" />
-                  </label>
-                  <div v-if="loanPaymentAmount > 0" class="loan-breakdown">
+                  <!-- 원리금균등: 납입금액 직접 입력 -->
+                  <template v-if="loanAutoResult?.needsInput">
+                    <label>납입금액(원리금균등)
+                      <input v-model.number="loanPaymentAmount" type="number" min="0"
+                        placeholder="이번 달 납입할 총금액" :disabled="submitting" />
+                    </label>
+                  </template>
+                  <!-- 원금균등·만기일시: 자동계산 결과 표시 -->
+                  <template v-else>
+                    <div class="loan-breakdown">
+                      <span class="bd-label">{{ repayTargetLoanWallet.loanMethod === 'BULLET' ? '만기일시' : '원금균등' }} 자동계산</span>
+                      <span>납입 <b>{{ (loanAutoResult?.total || 0).toLocaleString('ko-KR') }}원</b></span>
+                    </div>
+                  </template>
+                  <!-- 계산 결과 표시 + 수동 조정 -->
+                  <div v-if="(form.interest ?? null) !== null || (form.principal ?? null) !== null" class="loan-breakdown">
                     <span>이자 <b>{{ (form.interest || 0).toLocaleString('ko-KR') }}원</b></span>
-                    <span>원금상환 <b>{{ (form.principal || 0).toLocaleString('ko-KR') }}원</b></span>
+                    <span>원금 <b>{{ (form.principal || 0).toLocaleString('ko-KR') }}원</b></span>
                   </div>
                   <label>이자(조정)<input v-model.number="form.interest" type="number" min="0" :disabled="submitting" /></label>
                   <label>원금(조정)<input v-model.number="form.principal" type="number" min="0" :disabled="submitting" /></label>
@@ -2027,6 +2061,12 @@ button.primary {
 .loan-breakdown b {
   color: hsla(160, 100%, 37%, 1);
 }
+.loan-breakdown .bd-label {
+  width: 100%;
+  font-size: 0.78rem;
+  opacity: 0.6;
+  margin-bottom: 0.1rem;
+}
 .tag-field {
   display: flex;
   flex-direction: column;