fix(payment): integrate recharge fee rate in order flow and fix UI display

Backend:
- Use cfg.RechargeFeeRate in order creation instead of hardcoded 0
- Remove dead getFeeRate stub method
- All amounts computed server-side: order_amount, pay_amount, fee_rate

Frontend - PaymentView:
- Read recharge_fee_rate from checkout-info API (not per-method)
- Show fee breakdown only when fee_rate > 0
- Show credited amount only when multiplier ≠ 1

Frontend - Order display (user + admin):
- Fix fee_rate * 100 bug (fee_rate is already a percentage)
- OrderTable: show pay_amount as primary, fee/credited as sub-lines
- AdminOrderDetail: full breakdown (base/fee/paid/credited)
- AdminRefundDialog: label "到账金额" for clarity
- PaymentResultView: show pay_amount with fee info

Types + i18n:
- Add recharge_fee_rate to CheckoutInfoResponse
- Add fee_rate to CreateOrderResult
- Add translations: creditedAmount, fee, baseAmount, includedInPayAmount

frontend/src/components/payment/OrderTable.vue

@@ -12,10 +12,15 @@
         <span v-if="row.user_notes" class="ml-1 text-xs text-gray-400">({{ row.user_notes }})</span>
       </div>
     </template>
-    <template #cell-amount="{ value, row }">
+    <template #cell-pay_amount="{ value, row }">
       <div class="text-sm">
-        <span class="font-medium text-gray-900 dark:text-white">{{ row.order_type === 'balance' ? '$' : '¥' }}{{ value.toFixed(2) }}</span>
-        <span v-if="row.pay_amount !== value" class="ml-1 text-xs text-gray-500">(¥{{ row.pay_amount.toFixed(2) }})</span>
+        <span class="font-medium text-gray-900 dark:text-white">¥{{ value.toFixed(2) }}</span>
+        <span v-if="row.fee_rate > 0" class="ml-1 text-xs text-gray-400" :title="t('payment.orders.fee') + ': ' + row.fee_rate + '%'">
+          ({{ t('payment.orders.fee') }} {{ row.fee_rate }}%)
+        </span>
+        <div v-if="row.amount !== row.pay_amount" class="text-xs text-gray-500">
+          {{ t('payment.orders.creditedAmount') }}: {{ row.order_type === 'balance' ? '$' : '¥' }}{{ row.amount.toFixed(2) }}
+        </div>
       </div>
     </template>
     <template #cell-payment_type="{ value }">
@@ -60,7 +65,7 @@ const columns = computed((): Column[] => {
     cols.push({ key: 'user_email', label: t('payment.admin.colUser') })
   }
   cols.push(
-    { key: 'amount', label: t('payment.orders.amount') },
+    { key: 'pay_amount', label: t('payment.orders.payAmount') },
     { key: 'payment_type', label: t('payment.orders.paymentMethod') },
     { key: 'status', label: t('payment.orders.status') },
     { key: 'created_at', label: t('payment.orders.createdAt') },