feat: 归档佣金计算触发和快照变更，同步规范文档

- 归档 OpenSpec 变更到 archive 目录
- 创建 2 个新的主规范文件：commission-trigger 和 order-commission-snapshot
- 实现订单佣金快照字段和支付自动触发
- 确保事务一致性，所有佣金操作在同一事务内完成
- 提取成本价计算为公共工具函数

pkg/utils/commission.go

@@ -0,0 +1,13 @@
+package utils
+
+import "github.com/break/junhong_cmp_fiber/internal/model"
+
+func CalculateCostPrice(allocation *model.ShopSeriesAllocation, orderAmount int64) int64 {
+	if allocation.BaseCommissionMode == model.CommissionModeFixed {
+		return orderAmount - allocation.BaseCommissionValue
+	} else if allocation.BaseCommissionMode == model.CommissionModePercent {
+		commission := orderAmount * allocation.BaseCommissionValue / 1000
+		return orderAmount - commission
+	}
+	return orderAmount
+}