Auto-populate loan details from Plaid liabilities and pre-fill setup form

Fetch loan data (mortgage/student) from Plaid's Liabilities API during sync
and auto-create LoanDetail records. For accounts without liabilities data,
pre-populate the setup form with balance, interest rate, and smart term
defaults. Also fixes maturity date computation in the frontend form.

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

frontend/src/views/loans/LoansView.vue

@@ -215,6 +215,9 @@
       <v-card>
         <v-card-title>{{ editingLoan ? 'Edit' : 'Set Up' }} Loan Details</v-card-title>
         <v-card-text>
+          <v-alert v-if="prePopulated && !editingLoan" type="info" variant="tonal" density="compact" class="mb-4">
+            Some fields have been pre-populated from your bank sync data. Please review and adjust as needed.
+          </v-alert>
           <v-text-field v-model.number="loanForm.originalBalance" label="Original Balance" type="number" prefix="$" />
           <v-text-field v-model.number="loanForm.interestRate" label="Interest Rate (%)" type="number" suffix="%" step="0.125" />
           <v-text-field v-model.number="loanForm.termMonths" label="Term (months)" type="number" />
@@ -242,7 +245,7 @@ import { useRouter } from 'vue-router'
 import { loansApi } from '@/services/loans'
 import { useAccountsStore } from '@/stores/accounts'
 import { formatCurrency, formatDate, accountTypeIcon } from '@/utils/formatters'
-import type { LoanDetail, PayoffScenario } from '@/types'
+import type { LoanDefaults, LoanDetail, PayoffScenario } from '@/types'
 
 const props = defineProps<{ id?: string }>()
 const router = useRouter()
@@ -256,6 +259,7 @@ const calculatingPayoff = ref(false)
 const showLoanDialog = ref(false)
 const showSetup = ref(false)
 const editingLoan = ref(false)
+const prePopulated = ref(false)
 const snackbar = ref(false)
 const snackbarText = ref('')
 const snackbarColor = ref('success')
@@ -316,8 +320,9 @@ async function loadLoanDetail() {
   }
 }
 
-function openSetupDialog() {
+async function openSetupDialog() {
   editingLoan.value = false
+  prePopulated.value = false
   loanForm.value = {
     originalBalance: 0,
     interestRate: 0,
@@ -327,6 +332,19 @@ function openSetupDialog() {
     escrowAmount: null,
     extraPayment: null,
   }
+
+  if (props.id) {
+    try {
+      const { data } = await loansApi.getLoanDefaults(props.id)
+      if (data.originalBalance > 0) loanForm.value.originalBalance = data.originalBalance
+      if (data.interestRate > 0) loanForm.value.interestRate = data.interestRate
+      if (data.termMonths > 0) loanForm.value.termMonths = data.termMonths
+      prePopulated.value = data.hasSyncData
+    } catch {
+      // Fall back to zero defaults
+    }
+  }
+
   showLoanDialog.value = true
 }
 
@@ -349,8 +367,13 @@ async function saveLoanDetail() {
   if (!props.id) return
   saving.value = true
   try {
+    const originDate = new Date(loanForm.value.originationDate)
+    const maturityDate = new Date(originDate)
+    maturityDate.setMonth(maturityDate.getMonth() + loanForm.value.termMonths)
+
     const payload = {
       ...loanForm.value,
+      maturityDate: maturityDate.toISOString(),
       escrowAmount: loanForm.value.escrowAmount || undefined,
       extraPayment: loanForm.value.extraPayment || undefined,
     }