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/model/dto/my_commission_dto.go

@@ -41,7 +41,7 @@ type MyWithdrawalListReq struct {
 type MyCommissionRecordListReq struct {
 	Page             int     `json:"page" query:"page" validate:"omitempty,min=1" minimum:"1" description:"页码"`
 	PageSize         int     `json:"page_size" query:"page_size" validate:"omitempty,min=1,max=100" minimum:"1" maximum:"100" description:"每页数量"`
-	CommissionSource *string `json:"commission_source" query:"commission_source" validate:"omitempty,oneof=cost_diff one_time tier_bonus" description:"佣金来源 (cost_diff:成本价差, one_time:一次性佣金, tier_bonus:梯度奖励)"`
+	CommissionSource *string `json:"commission_source" query:"commission_source" validate:"omitempty,oneof=cost_diff one_time tier_bonus" description:"佣金来源 (cost_diff:成本价差, one_time:一次性佣金, tier_bonus(已废弃):梯度奖励)"`
 	ICCID            string  `json:"iccid" query:"iccid" description:"ICCID（模糊查询）"`
 	DeviceNo         string  `json:"device_no" query:"device_no" description:"设备号（模糊查询）"`
 	OrderNo          string  `json:"order_no" query:"order_no" description:"订单号（模糊查询）"`
@@ -51,7 +51,7 @@ type MyCommissionRecordItem struct {
 	ID               uint   `json:"id" description:"佣金记录ID"`
 	ShopID           uint   `json:"shop_id" description:"店铺ID"`
 	OrderID          uint   `json:"order_id" description:"订单ID"`
-	CommissionSource string `json:"commission_source" description:"佣金来源 (cost_diff:成本价差, one_time:一次性佣金, tier_bonus:梯度奖励)"`
+	CommissionSource string `json:"commission_source" description:"佣金来源 (cost_diff:成本价差, one_time:一次性佣金, tier_bonus(已废弃):梯度奖励)"`
 	Amount           int64  `json:"amount" description:"佣金金额（分）"`
 	Status           int    `json:"status" description:"状态 (1:已入账, 2:已失效)"`
 	StatusName       string `json:"status_name" description:"状态名称"`