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

backend/internal/service/payment_order.go

@@ -51,7 +51,7 @@ func (s *PaymentService) CreateOrder(ctx context.Context, req CreateOrderRequest
 	} else if req.OrderType == payment.OrderTypeBalance {
 		orderAmount = calculateCreditedBalance(req.Amount, cfg.BalanceRechargeMultiplier)
 	}
-	feeRate := s.getFeeRate(req.PaymentType)
+	feeRate := cfg.RechargeFeeRate
 	payAmountStr := payment.CalculatePayAmount(limitAmount, feeRate)
 	payAmount, _ := strconv.ParseFloat(payAmountStr, 64)
 	order, err := s.createOrderInTx(ctx, req, user, plan, cfg, orderAmount, limitAmount, feeRate, payAmount)

backend/internal/service/payment_service.go

@@ -288,7 +288,6 @@ func psComputeValidityDays(days int, unit string) int {
 	}
 }
 
-func (s *PaymentService) getFeeRate(_ string) float64 { return 0 }
 
 func psStartOfDayUTC(t time.Time) time.Time {
 	y, m, d := t.UTC().Date()