清理冗余的梯度返佣(TierCommission)配置

- 移除 Model 层：删除 ShopSeriesCommissionTier 模型及相关字段
- 更新 DTO：删除 TierCommissionConfig、TierEntry 类型及相关请求/响应字段
- 删除 Store 层：移除 ShopSeriesCommissionTierStore 及相关查询逻辑
- 简化 Service 层：删除梯度返佣处理逻辑，统计查询移除 tier_bonus 字段
- 数据库迁移：创建 000034_remove_tier_commission 移除相关表和字段
- 更新测试：移除梯度返佣相关测试用例，更新集成测试
- OpenAPI 文档：删除梯度返佣相关 schema 和枚举值
- 归档变更：归档 remove-tier-commission-redundancy 到 archive/2026-01-30-
- 同步规范：更新 4 个主 specs，标记废弃功能并添加迁移指引

原因：梯度返佣功能与一次性梯度佣金功能重复，且从未实现实际计算逻辑
迁移：使用一次性佣金的梯度模式 (OneTimeCommissionConfig.type = "tiered") 替代

internal/service/package/service.go

@@ -21,7 +21,6 @@ type Service struct {
 	packageSeriesStore     *postgres.PackageSeriesStore
 	packageAllocationStore *postgres.ShopPackageAllocationStore
 	seriesAllocationStore  *postgres.ShopSeriesAllocationStore
-	commissionTierStore    *postgres.ShopSeriesCommissionTierStore
 }
 
 func New(
@@ -29,14 +28,12 @@ func New(
 	packageSeriesStore *postgres.PackageSeriesStore,
 	packageAllocationStore *postgres.ShopPackageAllocationStore,
 	seriesAllocationStore *postgres.ShopSeriesAllocationStore,
-	commissionTierStore *postgres.ShopSeriesCommissionTierStore,
 ) *Service {
 	return &Service{
 		packageStore:           packageStore,
 		packageSeriesStore:     packageSeriesStore,
 		packageAllocationStore: packageAllocationStore,
 		seriesAllocationStore:  seriesAllocationStore,
-		commissionTierStore:    commissionTierStore,
 	}
 }
 
@@ -404,20 +401,5 @@ func (s *Service) getCommissionInfo(ctx context.Context, allocationID uint) *dto
 		info.CurrentRate = fmt.Sprintf("%.1f%%", float64(seriesAllocation.BaseCommissionValue)/10)
 	}
 
-	if seriesAllocation.EnableTierCommission {
-		tiers, err := s.commissionTierStore.ListByAllocationID(ctx, allocationID)
-		if err == nil && len(tiers) > 0 {
-			tier := tiers[0]
-			info.NextThreshold = &tier.ThresholdValue
-			if tier.CommissionMode == constants.CommissionModeFixed {
-				nextRate := fmt.Sprintf("%.2f元/单", float64(tier.CommissionValue)/100)
-				info.NextRate = nextRate
-			} else {
-				nextRate := fmt.Sprintf("%.1f%%", float64(tier.CommissionValue)/10)
-				info.NextRate = nextRate
-			}
-		}
-	}
-
 	return info
 }