feat(payment): 充值赠送阶梯（按金额档位额外赠送到账额度）

- 后台支付设置新增「充值赠送阶梯」（满 X 送 Y%，RECHARGE_BONUS_TIERS）与 Markdown 活动文案
  （RECHARGE_BONUS_NOTICE）：阈值按用户输入的支付金额命中（取不超过金额的最大档），
  赠送按到账基数（输入 × 充值倍率）计算；严格校验写入、宽松解析读取，订阅订单不参与
- 下单时按当时配置计算赠送并落库：payment_orders 新增 bonus_amount 列（迁移 241），
  amount 仍为到账总额，到账/兑换码/退款逻辑不变；推广返利基数改为 amount - bonus_amount
- checkout-info 下发 recharge_bonus_tiers / recharge_bonus_notice；创建订单与订单查询响应带 bonus_amount
- 充值页：快捷金额按钮右上角「+N%」角标 + 第二行到账金额，金额卡顶部渲染活动文案，
  订单摘要新增赠送额度行并在有赠送时始终显示到账余额；订单列表/详情/支付结果/成功面板显示含赠送
- 后台新增 RechargeBonusTierEditor（行内校验重复/非法阈值，自动排序并显示区间预览）
- 补后端单测、契约测试与前端 vitest，zh/en 文案

backend/ent/runtime/runtime.go

@@ -1323,70 +1323,74 @@ func init() {
 	paymentorderDescFeeRate := paymentorderFields[6].Descriptor()
 	// paymentorder.DefaultFeeRate holds the default value on creation for the fee_rate field.
 	paymentorder.DefaultFeeRate = paymentorderDescFeeRate.Default.(float64)
+	// paymentorderDescBonusAmount is the schema descriptor for bonus_amount field.
+	paymentorderDescBonusAmount := paymentorderFields[7].Descriptor()
+	// paymentorder.DefaultBonusAmount holds the default value on creation for the bonus_amount field.
+	paymentorder.DefaultBonusAmount = paymentorderDescBonusAmount.Default.(float64)
 	// paymentorderDescRechargeCode is the schema descriptor for recharge_code field.
-	paymentorderDescRechargeCode := paymentorderFields[7].Descriptor()
+	paymentorderDescRechargeCode := paymentorderFields[8].Descriptor()
 	// paymentorder.RechargeCodeValidator is a validator for the "recharge_code" field. It is called by the builders before save.
 	paymentorder.RechargeCodeValidator = paymentorderDescRechargeCode.Validators[0].(func(string) error)
 	// paymentorderDescOutTradeNo is the schema descriptor for out_trade_no field.
-	paymentorderDescOutTradeNo := paymentorderFields[8].Descriptor()
+	paymentorderDescOutTradeNo := paymentorderFields[9].Descriptor()
 	// paymentorder.DefaultOutTradeNo holds the default value on creation for the out_trade_no field.
 	paymentorder.DefaultOutTradeNo = paymentorderDescOutTradeNo.Default.(string)
 	// paymentorder.OutTradeNoValidator is a validator for the "out_trade_no" field. It is called by the builders before save.
 	paymentorder.OutTradeNoValidator = paymentorderDescOutTradeNo.Validators[0].(func(string) error)
 	// paymentorderDescPaymentType is the schema descriptor for payment_type field.
-	paymentorderDescPaymentType := paymentorderFields[9].Descriptor()
+	paymentorderDescPaymentType := paymentorderFields[10].Descriptor()
 	// paymentorder.PaymentTypeValidator is a validator for the "payment_type" field. It is called by the builders before save.
 	paymentorder.PaymentTypeValidator = paymentorderDescPaymentType.Validators[0].(func(string) error)
 	// paymentorderDescPaymentTradeNo is the schema descriptor for payment_trade_no field.
-	paymentorderDescPaymentTradeNo := paymentorderFields[10].Descriptor()
+	paymentorderDescPaymentTradeNo := paymentorderFields[11].Descriptor()
 	// paymentorder.PaymentTradeNoValidator is a validator for the "payment_trade_no" field. It is called by the builders before save.
 	paymentorder.PaymentTradeNoValidator = paymentorderDescPaymentTradeNo.Validators[0].(func(string) error)
 	// paymentorderDescOrderType is the schema descriptor for order_type field.
-	paymentorderDescOrderType := paymentorderFields[14].Descriptor()
+	paymentorderDescOrderType := paymentorderFields[15].Descriptor()
 	// paymentorder.DefaultOrderType holds the default value on creation for the order_type field.
 	paymentorder.DefaultOrderType = paymentorderDescOrderType.Default.(string)
 	// paymentorder.OrderTypeValidator is a validator for the "order_type" field. It is called by the builders before save.
 	paymentorder.OrderTypeValidator = paymentorderDescOrderType.Validators[0].(func(string) error)
 	// paymentorderDescProviderInstanceID is the schema descriptor for provider_instance_id field.
-	paymentorderDescProviderInstanceID := paymentorderFields[18].Descriptor()
+	paymentorderDescProviderInstanceID := paymentorderFields[19].Descriptor()
 	// paymentorder.ProviderInstanceIDValidator is a validator for the "provider_instance_id" field. It is called by the builders before save.
 	paymentorder.ProviderInstanceIDValidator = paymentorderDescProviderInstanceID.Validators[0].(func(string) error)
 	// paymentorderDescProviderKey is the schema descriptor for provider_key field.
-	paymentorderDescProviderKey := paymentorderFields[19].Descriptor()
+	paymentorderDescProviderKey := paymentorderFields[20].Descriptor()
 	// paymentorder.ProviderKeyValidator is a validator for the "provider_key" field. It is called by the builders before save.
 	paymentorder.ProviderKeyValidator = paymentorderDescProviderKey.Validators[0].(func(string) error)
 	// paymentorderDescStatus is the schema descriptor for status field.
-	paymentorderDescStatus := paymentorderFields[21].Descriptor()
+	paymentorderDescStatus := paymentorderFields[22].Descriptor()
 	// paymentorder.DefaultStatus holds the default value on creation for the status field.
 	paymentorder.DefaultStatus = paymentorderDescStatus.Default.(string)
 	// paymentorder.StatusValidator is a validator for the "status" field. It is called by the builders before save.
 	paymentorder.StatusValidator = paymentorderDescStatus.Validators[0].(func(string) error)
 	// paymentorderDescRefundAmount is the schema descriptor for refund_amount field.
-	paymentorderDescRefundAmount := paymentorderFields[22].Descriptor()
+	paymentorderDescRefundAmount := paymentorderFields[23].Descriptor()
 	// paymentorder.DefaultRefundAmount holds the default value on creation for the refund_amount field.
 	paymentorder.DefaultRefundAmount = paymentorderDescRefundAmount.Default.(float64)
 	// paymentorderDescForceRefund is the schema descriptor for force_refund field.
-	paymentorderDescForceRefund := paymentorderFields[25].Descriptor()
+	paymentorderDescForceRefund := paymentorderFields[26].Descriptor()
 	// paymentorder.DefaultForceRefund holds the default value on creation for the force_refund field.
 	paymentorder.DefaultForceRefund = paymentorderDescForceRefund.Default.(bool)
 	// paymentorderDescRefundRequestedBy is the schema descriptor for refund_requested_by field.
-	paymentorderDescRefundRequestedBy := paymentorderFields[28].Descriptor()
+	paymentorderDescRefundRequestedBy := paymentorderFields[29].Descriptor()
 	// paymentorder.RefundRequestedByValidator is a validator for the "refund_requested_by" field. It is called by the builders before save.
 	paymentorder.RefundRequestedByValidator = paymentorderDescRefundRequestedBy.Validators[0].(func(string) error)
 	// paymentorderDescClientIP is the schema descriptor for client_ip field.
-	paymentorderDescClientIP := paymentorderFields[34].Descriptor()
+	paymentorderDescClientIP := paymentorderFields[35].Descriptor()
 	// paymentorder.ClientIPValidator is a validator for the "client_ip" field. It is called by the builders before save.
 	paymentorder.ClientIPValidator = paymentorderDescClientIP.Validators[0].(func(string) error)
 	// paymentorderDescSrcHost is the schema descriptor for src_host field.
-	paymentorderDescSrcHost := paymentorderFields[35].Descriptor()
+	paymentorderDescSrcHost := paymentorderFields[36].Descriptor()
 	// paymentorder.SrcHostValidator is a validator for the "src_host" field. It is called by the builders before save.
 	paymentorder.SrcHostValidator = paymentorderDescSrcHost.Validators[0].(func(string) error)
 	// paymentorderDescCreatedAt is the schema descriptor for created_at field.
-	paymentorderDescCreatedAt := paymentorderFields[37].Descriptor()
+	paymentorderDescCreatedAt := paymentorderFields[38].Descriptor()
 	// paymentorder.DefaultCreatedAt holds the default value on creation for the created_at field.
 	paymentorder.DefaultCreatedAt = paymentorderDescCreatedAt.Default.(func() time.Time)
 	// paymentorderDescUpdatedAt is the schema descriptor for updated_at field.
-	paymentorderDescUpdatedAt := paymentorderFields[38].Descriptor()
+	paymentorderDescUpdatedAt := paymentorderFields[39].Descriptor()
 	// paymentorder.DefaultUpdatedAt holds the default value on creation for the updated_at field.
 	paymentorder.DefaultUpdatedAt = paymentorderDescUpdatedAt.Default.(func() time.Time)
 	// paymentorder.UpdateDefaultUpdatedAt holds the default value on update for the updated_at field.