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/i18n/locales/zh.ts

@@ -5575,6 +5575,10 @@ export default {
       orderNo: '订单编号',
       amount: '金额',
       payAmount: '实付',
+      creditedAmount: '到账金额',
+      fee: '手续费',
+      baseAmount: '充值金额',
+      includedInPayAmount: '已含在实付金额中',
       status: '状态',
       paymentMethod: '支付方式',
       createdAt: '创建时间',