feat(checkout): 修复后置损耗结算全额归号主、支持角色隔离实时试算与全流程UI重构

- fix(pricing): 后置消耗/损耗金额 100% 划归号主收益，超出预收部分平台不抽成，避免被平台费吸收
- feat(checkout): 前端新增结账实时试算预览组件 (CheckoutTrialPreview + useCheckoutSimulator)，角色隔离展示（仅见自身收入/退款，屏蔽平台服务费）
- refactor(admin): 重构交易全流程时间线 (ProcessTimeline.vue)，将平铺挤压指标重构成4大分类仪表盘微型卡片矩阵，升级可视化业务状态流转徽章与阶段色彩主题
- style(admin): 优化支付与交接流水元信息网格布局，防止超宽屏下长单行拉伸

backend/internal/modules/order/pricing.go

@@ -336,16 +336,22 @@ func calculateCheckoutSettlement(order model.RentalOrder, consumableAmountCent i
 		}
 	}
 
-	// 消耗品按申报金额计价，允许超过预收；号主侧按预收消耗品占比线性外推
+	// 消耗品按申报金额计价，允许超过预收；号主侧按预收消耗品占比外推，超额及无预收损耗全额归号主
 	usedBuyerConsumablePriceCent := maxCent(consumableAmountCent, 0)
-	consumableUseRatio := 0.0
+	var usedOwnerConsumablePriceCent int64
 	if prepaidConsumablePriceCent > 0 {
-		consumableUseRatio = maxRatio(float64(usedBuyerConsumablePriceCent)/float64(prepaidConsumablePriceCent), 0)
-	}
-	usedOwnerConsumablePriceCent := int64(math.Round(float64(prepaidOwnerConsumablePriceCent) * consumableUseRatio))
-	if usedBuyerConsumablePriceCent <= prepaidConsumablePriceCent {
-		usedBuyerConsumablePriceCent = minCent(usedBuyerConsumablePriceCent, prepaidConsumablePriceCent)
-		usedOwnerConsumablePriceCent = minCent(usedOwnerConsumablePriceCent, prepaidOwnerConsumablePriceCent)
+		if usedBuyerConsumablePriceCent <= prepaidConsumablePriceCent {
+			consumableUseRatio := maxRatio(float64(usedBuyerConsumablePriceCent)/float64(prepaidConsumablePriceCent), 0)
+			usedOwnerConsumablePriceCent = int64(math.Round(float64(prepaidOwnerConsumablePriceCent) * consumableUseRatio))
+			usedOwnerConsumablePriceCent = minCent(usedOwnerConsumablePriceCent, prepaidOwnerConsumablePriceCent)
+		} else {
+			// 预收范围内按号主预收基准，超出预收部分作为后置损耗全额划归号主（平台不抽成）
+			excessCent := usedBuyerConsumablePriceCent - prepaidConsumablePriceCent
+			usedOwnerConsumablePriceCent = prepaidOwnerConsumablePriceCent + excessCent
+		}
+	} else {
+		// 原订单无预收消耗品，后置申报的消耗/损耗金额 100% 归号主，平台不抽成
+		usedOwnerConsumablePriceCent = usedBuyerConsumablePriceCent
 	}
 
 	pureCoinPlatformFeeCent := maxCent(usedBuyerCoinPriceCent-usedOwnerCoinPriceCent, 0)