feat(distribution): 补齐退款加价回退、本站自卖与开通默认规则

退款时压缩卖方加价，人工/自动批次仅完结单可入账，号主收入进主站钱包；仲裁后重算释放并支持作废未入账 DS。开通时四种模式按默认生效，对外口径合并为 35/40/25，不再单独展示通道费。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/modules/distribution/dto.go

@@ -333,7 +333,7 @@ type OnboardSiteRequest struct {
 	AdminPassword           string  `json:"admin_password" binding:"required,min=6,max=64"`
 	AdminNickname           string  `json:"admin_nickname"`
 	MemberType              string  `json:"member_type" binding:"omitempty,oneof=operator finance customer_service"`
-	DistributorReceiveRatio float64 `json:"distributor_receive_ratio"`
+	DistributorReceiveRatio float64 `json:"distributor_receive_ratio"` // 兼容旧入参，开通时忽略，四种模式一律走默认分成
 	PlatformSellRatio       float64 `json:"platform_sell_ratio"`
 	ServiceFeeValue         float64 `json:"service_fee_value"`
 }
@@ -417,6 +417,7 @@ type SiteWalletDTO struct {
 	PendingReleaseCent   int64  `json:"pending_release_cent"`
 	TotalSettledCent     int64  `json:"total_settled_cent"`
 	TotalWithdrawnCent   int64  `json:"total_withdrawn_cent"`
+	SettlementHoldDays   int    `json:"settlement_hold_days"`
 }
 
 type ApplySiteWithdrawalRequest struct {