feat(payment): i18n payment error codes and label localization

Pairs with the backend structured payment errors (reason + metadata). The
frontend now maps reason codes to localized messages with metadata as
interpolation variables, and automatically localizes raw config-field names
(e.g. "certSerial" → "证书序列号") using the existing UI-label i18n
namespace.

- frontend/src/utils/apiError.ts
  - extractApiErrorCode now prefers the string `reason` over the numeric HTTP
    `code`; reason is granular enough to drive i18n lookup, HTTP code is not.
  - New extractApiErrorMetadata to pull interpolation params off the error.
  - New extractI18nErrorMessage(err, t, namespace, fallback): looks up
    `<namespace>.<REASON>` in i18n and substitutes metadata. Before
    substitution, `metadata.key` and `metadata.keys` (slash-joined) are
    re-translated through `admin.settings.payment.field_<key>` so users see
    "缺少必填项：证书序列号" instead of "缺少必填项：certSerial".

- frontend/src/i18n/locales/{zh,en}.ts
  - Add payment.errors entries for every structured reason code returned by
    the backend (PAYMENT_DISABLED, INVALID_AMOUNT, TOO_MANY_PENDING,
    DAILY_LIMIT_EXCEEDED, NO_AVAILABLE_INSTANCE, PAYMENT_PROVIDER_MISCONFIGURED,
    WXPAY_CONFIG_MISSING_KEY / INVALID_KEY_LENGTH / INVALID_KEY, NOT_FOUND,
    FORBIDDEN, CONFLICT, INVALID_ORDER_TYPE, INVALID_STATUS,
    BALANCE_NOT_ENOUGH, REFUND_AMOUNT_EXCEEDED, REFUND_FAILED, and more),
    with placeholders for template variables.

- 13 payment-related Vue files
  - Migrate catch-block error reporting from extractApiErrorMessage to
    extractI18nErrorMessage(err, t, 'payment.errors', fallback).
  - Remove the ad-hoc paymentErrorMap computed in SettingsView.vue, which the
    new helper supersedes (it reads i18n directly via t).

- frontend/src/components/payment/providerConfig.ts
  - wxpay: publicKey and publicKeyId are now required (was optional), matching
    the pubkey-only verifier direction; certSerial is already required.

This PR is drop-in safe: reason-preferring extractApiErrorCode is backward
compatible with callers that pass their own i18nMap, and error codes missing
from i18n fall back to the existing message-based path.

frontend/src/views/admin/orders/AdminOrdersView.vue

@@ -116,7 +116,7 @@ import { ref, reactive, computed, onMounted } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { useAppStore } from '@/stores/app'
 import { adminPaymentAPI } from '@/api/admin/payment'
-import { extractApiErrorMessage } from '@/utils/apiError'
+import { extractI18nErrorMessage } from '@/utils/apiError'
 import { formatOrderDateTime } from '@/components/payment/orderUtils'
 import type { PaymentOrder } from '@/types/payment'
 import AppLayout from '@/components/layout/AppLayout.vue'
@@ -167,7 +167,7 @@ async function loadOrders() {
     orders.value = res.data.items || []
     orderPagination.total = res.data.total || 0
   } catch (err: unknown) {
-    appStore.showError(extractApiErrorMessage(err, t('common.error')))
+    appStore.showError(extractI18nErrorMessage(err, t, 'payment.errors', t('common.error')))
   } finally { ordersLoading.value = false }
 }
 
@@ -214,12 +214,12 @@ async function showOrderDetail(order: PaymentOrder) {
 
 async function handleCancelOrder(order: PaymentOrder) {
   try { await adminPaymentAPI.cancelOrder(order.id); appStore.showSuccess(t('payment.admin.orderCancelled')); loadOrders() }
-  catch (err: unknown) { appStore.showError(extractApiErrorMessage(err, t('common.error'))) }
+  catch (err: unknown) { appStore.showError(extractI18nErrorMessage(err, t, 'payment.errors', t('common.error'))) }
 }
 
 async function handleRetryOrder(order: PaymentOrder) {
   try { await adminPaymentAPI.retryRecharge(order.id); appStore.showSuccess(t('payment.admin.retrySuccess')); loadOrders() }
-  catch (err: unknown) { appStore.showError(extractApiErrorMessage(err, t('common.error'))) }
+  catch (err: unknown) { appStore.showError(extractI18nErrorMessage(err, t, 'payment.errors', t('common.error'))) }
 }
 
 function openRefundDialog(order: PaymentOrder) { selectedOrder.value = order; showRefundDialog.value = true }
@@ -230,7 +230,7 @@ async function handleRefund(data: { amount: number; reason: string; deduct_balan
   try {
     await adminPaymentAPI.refundOrder(selectedOrder.value.id, { amount: data.amount, reason: data.reason, deduct_balance: data.deduct_balance, force: data.force })
     appStore.showSuccess(t('payment.admin.refundSuccess')); showRefundDialog.value = false; loadOrders()
-  } catch (err: unknown) { appStore.showError(extractApiErrorMessage(err, t('common.error'))) }
+  } catch (err: unknown) { appStore.showError(extractI18nErrorMessage(err, t, 'payment.errors', t('common.error'))) }
   finally { refundSubmitting.value = false }
 }
 

frontend/src/views/admin/orders/AdminPaymentDashboardView.vue

@@ -72,7 +72,7 @@ import { ref, watch, onMounted } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { useAppStore } from '@/stores/app'
 import { adminPaymentAPI } from '@/api/admin/payment'
-import { extractApiErrorMessage } from '@/utils/apiError'
+import { extractI18nErrorMessage } from '@/utils/apiError'
 import type { DashboardStats } from '@/types/payment'
 import AppLayout from '@/components/layout/AppLayout.vue'
 import LoadingSpinner from '@/components/common/LoadingSpinner.vue'
@@ -110,7 +110,7 @@ async function loadDashboard() {
     const res = await adminPaymentAPI.getDashboard(days.value)
     stats.value = res.data
   } catch (err: unknown) {
-    appStore.showError(extractApiErrorMessage(err, t('common.error')))
+    appStore.showError(extractI18nErrorMessage(err, t, 'payment.errors', t('common.error')))
   } finally {
     loading.value = false
   }

frontend/src/views/admin/orders/AdminPaymentPlansView.vue

@@ -78,7 +78,7 @@ import { ref, computed, onMounted } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { useAppStore } from '@/stores/app'
 import { adminPaymentAPI } from '@/api/admin/payment'
-import { extractApiErrorMessage } from '@/utils/apiError'
+import { extractI18nErrorMessage } from '@/utils/apiError'
 import adminAPI from '@/api/admin'
 import type { SubscriptionPlan } from '@/types/payment'
 import type { AdminGroup } from '@/types'
@@ -150,7 +150,7 @@ async function loadPlans() {
         : (p.features || []),
     }))
   }
-  catch (err: unknown) { appStore.showError(extractApiErrorMessage(err, t('common.error'))) }
+  catch (err: unknown) { appStore.showError(extractI18nErrorMessage(err, t, 'payment.errors', t('common.error'))) }
   finally { plansLoading.value = false }
 }
 
@@ -166,7 +166,7 @@ async function toggleForSale(plan: SubscriptionPlan) {
     await adminPaymentAPI.updatePlan(plan.id, { for_sale: !plan.for_sale })
     plan.for_sale = !plan.for_sale
   } catch (err: unknown) {
-    appStore.showError(extractApiErrorMessage(err, t('common.error')))
+    appStore.showError(extractI18nErrorMessage(err, t, 'payment.errors', t('common.error')))
   }
 }
 
@@ -174,7 +174,7 @@ function confirmDeletePlan(plan: SubscriptionPlan) { deletingPlanId.value = plan
 async function handleDeletePlan() {
   if (!deletingPlanId.value) return
   try { await adminPaymentAPI.deletePlan(deletingPlanId.value); appStore.showSuccess(t('common.deleted')); showDeletePlanDialog.value = false; loadPlans() }
-  catch (err: unknown) { appStore.showError(extractApiErrorMessage(err, t('common.error'))) }
+  catch (err: unknown) { appStore.showError(extractI18nErrorMessage(err, t, 'payment.errors', t('common.error'))) }
 }
 
 // ==================== Lifecycle ====================