feat(fx): 환율 갱신 시각 표시 및 자동 업데이트 레이블

- 환율 자동조회 후 '방금 업데이트 / N분 전 / N시간 전' 표시
- 30초 간격 ticker로 레이블 자동 갱신
- 폼 열기/통화 변경 시 rateUpdatedAt 초기화

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

src/views/account/AccountView.vue

@@ -1,5 +1,5 @@
 <script setup>
-import { computed, nextTick, onMounted, reactive, ref, watch } from 'vue'
+import { computed, nextTick, onMounted, onUnmounted, reactive, ref, watch } from 'vue'
 import { accountApi } from '@/api/accountApi'
 import { reminders } from '@/native/reminders'
 import { useAuthStore } from '@/stores/auth'
@@ -99,14 +99,31 @@ watch([() => form.currency, () => form.foreignAmount, () => form.rate], () => {
   if (isForeign.value) form.amount = convertedKrw.value
 })
 const fxLoading = ref(false)
+const rateUpdatedAt = ref(null) // 환율 마지막 조회 시각(ms)
+const tickNow = ref(Date.now())
+let _fxTick = null
+onMounted(() => { _fxTick = setInterval(() => { tickNow.value = Date.now() }, 30_000) })
+onUnmounted(() => clearInterval(_fxTick))
+const rateAgeLabel = computed(() => {
+  if (!rateUpdatedAt.value || !isForeign.value) return null
+  const diff = Math.floor((tickNow.value - rateUpdatedAt.value) / 1000)
+  if (diff < 60) return '방금 업데이트'
+  if (diff < 3600) return `${Math.floor(diff / 60)}분 전`
+  if (diff < 86400) return `${Math.floor(diff / 3600)}시간 전`
+  return `${Math.floor(diff / 86400)}일 전`
+})
 async function fetchRate() {
   if (!isForeign.value || fxLoading.value) return
   fxLoading.value = true
   try {
     const res = await accountApi.fxRate(form.currency, 'KRW')
     // 환율은 소수점 4자리로 통일(입력폼 step·저장 정밀도 일치)
-    if (res?.rate != null) form.rate = Math.round(Number(res.rate) * 10000) / 10000
-    else formInfo.value = '환율을 가져오지 못했어요. 직접 입력해 주세요.'
+    if (res?.rate != null) {
+      form.rate = Math.round(Number(res.rate) * 10000) / 10000
+      rateUpdatedAt.value = res.updatedAt ? new Date(res.updatedAt).getTime() : Date.now()
+    } else {
+      formInfo.value = '환율을 가져오지 못했어요. 직접 입력해 주세요.'
+    }
   } catch {
     formInfo.value = '환율 조회에 실패했어요. 직접 입력해 주세요.'
   } finally {
@@ -120,6 +137,7 @@ function onCurrencyChange() {
   } else {
     form.foreignAmount = null
     form.rate = null
+    rateUpdatedAt.value = null
   }
 }
 // 계좌/카드 (repayTargetIsCard·repayTargetLoanWallet computed가 참조하므로 먼저 선언)
@@ -500,6 +518,7 @@ function openCreate() {
   editId.value = null
   editingPending.value = false
   Object.assign(form, { entryDate: todayStr(), type: 'EXPENSE', category: '', amount: null, memo: '', walletKind: 'BANK', walletId: '', toWalletKind: '', toWalletId: '', principal: null, interest: null, annualFee: null, installmentMonths: '', currency: 'KRW', foreignAmount: null, rate: null })
+  rateUpdatedAt.value = null
   selectedTagIds.value = []
   formError.value = null
   formInfo.value = ''
@@ -540,6 +559,7 @@ function openEdit(e) {
   const nameToId = {}
   tagOptions.value.forEach((t) => (nameToId[t.name] = t.id))
   selectedTagIds.value = (e.tags || []).map((n) => nameToId[n]).filter(Boolean)
+  rateUpdatedAt.value = null
   pasteDetected.value = null
   pasteModalOpen.value = false
   pasteText.value = ''
@@ -1212,6 +1232,7 @@ onMounted(async () => {
                     <input v-model.number="form.rate" type="number" min="0" step="0.0001" placeholder="원" :disabled="submitting" />
                     <button type="button" class="fx-auto" :disabled="submitting || fxLoading" @click="fetchRate">{{ fxLoading ? '…' : '↻ 자동' }}</button>
                   </div>
+                  <span v-if="rateAgeLabel" class="fx-age">{{ rateAgeLabel }}</span>
                 </div>
                 <span class="fx-krw">= ₩{{ (convertedKrw || 0).toLocaleString('ko-KR') }}</span>
               </div>
@@ -2130,6 +2151,11 @@ button.primary {
   font-size: 0.9rem;
   padding-bottom: 0.45rem;
 }
+.fx-age {
+  font-size: 0.7rem;
+  color: var(--color-text-soft, #999);
+  margin-top: 0.18rem;
+}
 .row-wallet {
   margin-right: 0.35rem;
   font-size: 0.75rem;