feat(repayment): 대출·카드할부 상환 조회 화면 (유료)

- 사이드바 '대출·할부 상환' 메뉴(프리미엄 잠금), /account/repayments 라우트
- 대출: 상환방식별(원리금균등·원금균등·만기일시) 남은 회차 상각 스케줄
- 카드 할부: 무이자 가정, 진행 중 할부 건별 남은 회차
- 회차별 원금·이자·합계 + 남은 잔액 표기, 이번 달/남은 총액 합계
- 계산은 프런트(utils/repayment.js), 지갑·카드 내역만으로 산출

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

src/components/layout/AppSidebar.vue

@@ -26,6 +26,7 @@ const icons = {
   users: '<path d="M17 21v-2a4 4 0 0 0-4-4H5a4 4 0 0 0-4 4v2"/><circle cx="9" cy="7" r="4"/><path d="M23 21v-2a4 4 0 0 0-3-3.87"/><path d="M16 3.13a4 4 0 0 1 0 7.75"/>',
   sliders: '<line x1="4" y1="21" x2="4" y2="14"/><line x1="4" y1="10" x2="4" y2="3"/><line x1="12" y1="21" x2="12" y2="12"/><line x1="12" y1="8" x2="12" y2="3"/><line x1="20" y1="21" x2="20" y2="16"/><line x1="20" y1="12" x2="20" y2="3"/><line x1="1" y1="14" x2="7" y2="14"/><line x1="9" y1="8" x2="15" y2="8"/><line x1="17" y1="16" x2="23" y2="16"/>',
   flag: '<path d="M4 15s1-1 4-1 5 2 8 2 4-1 4-1V3s-1 1-4 1-5-2-8-2-4 1-4 1z"/><line x1="4" y1="22" x2="4" y2="15"/>',
+  repay: '<polyline points="23 18 13.5 8.5 8.5 13.5 1 6"/><polyline points="17 18 23 18 23 12"/>',
 }
 </script>
 
@@ -59,6 +60,11 @@ const icons = {
           <svg class="menu-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" v-html="icons.wallets" />
           <span>계좌 관리</span>
         </RouterLink>
+        <RouterLink to="/account/repayments" class="menu-item">
+          <svg class="menu-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" v-html="icons.repay" />
+          <span>대출·할부 상환</span>
+          <span v-if="lockPremium" class="lock-badge">🔒</span>
+        </RouterLink>
         <RouterLink to="/account/categories" class="menu-item">
           <svg class="menu-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" v-html="icons.categories" />
           <span>분류 관리</span>