实现结账流程：替换旧归还逻辑为完整结账-修正-争议流程

- 新增 order_checkouts 表，支持结账明细（消耗/押金扣除/退回/号主入账）
- 租客发起结账 → 号主确认 → 已完成（正常路径）
- 号主修改结账 → 租客确认修正 → 已完成（修正路径）
- 结账阶段任一方发起争议 → 后台仲裁 → 已完成/已关闭/异常（争议路径）
- 争议模块适配结账争议类型，仲裁结果新增 mark_abnormal
- 超时任务适配新的 pending_checkout_confirm 状态
- 前端结账明细面板、发起结账/确认/修正/拒绝表单全部实现
- 移除旧的 SubmitReturn/ConfirmReturn 接口

backend/internal/modules/order/dto.go

@@ -27,6 +27,7 @@ type OrderDTO struct {
 	Status           string         `json:"status"`
 	HandoffStatus    string         `json:"handoff_status"`
 	SettlementStatus string         `json:"settlement_status"`
+	Checkout         *CheckoutDTO   `json:"checkout,omitempty"`
 	CreatedAt        time.Time      `json:"created_at"`
 	UpdatedAt        time.Time      `json:"updated_at"`
 }
@@ -39,8 +40,21 @@ type SubmitHandoffRequest struct {
 	Content string `json:"content" binding:"required"`
 }
 
-type SubmitReturnRequest struct {
-	Content string `json:"content" binding:"required"`
+type SubmitCheckoutRequest struct {
+	Content          string   `json:"content" binding:"required"`
+	ConsumableAmount float64  `json:"consumable_amount"`
+	CoinConsumedM    float64  `json:"coin_consumed_m"`
+	OtherAmount      float64  `json:"other_amount"`
+	EvidenceURLS     []string `json:"evidence_urls"`
+}
+
+type CounterCheckoutRequest struct {
+	ConsumableAmount    float64  `json:"consumable_amount"`
+	CoinConsumedM       float64  `json:"coin_consumed_m"`
+	OtherAmount         float64  `json:"other_amount"`
+	DepositDeductAmount float64  `json:"deposit_deduct_amount"`
+	Reason              string   `json:"reason" binding:"required"`
+	EvidenceURLS        []string `json:"evidence_urls"`
 }
 
 type AdminActionRequest struct {
@@ -63,3 +77,26 @@ type HandoffRecordDTO struct {
 	ConfirmedByOwnerAt  *time.Time `json:"confirmed_by_owner_at"`
 	CreatedAt           time.Time  `json:"created_at"`
 }
+
+type CheckoutDTO struct {
+	ID                    uint64     `json:"id"`
+	OrderID               uint64     `json:"order_id"`
+	InitiatedBy           uint64     `json:"initiated_by"`
+	Status                string     `json:"status"`
+	RentAmount            float64    `json:"rent_amount"`
+	DepositAmount         float64    `json:"deposit_amount"`
+	ConsumableAmount      float64    `json:"consumable_amount"`
+	CoinConsumedM         float64    `json:"coin_consumed_m"`
+	OtherAmount           float64    `json:"other_amount"`
+	DepositDeductAmount   float64    `json:"deposit_deduct_amount"`
+	RenterRefundAmount    float64    `json:"renter_refund_amount"`
+	OwnerIncomeAmount     float64    `json:"owner_income_amount"`
+	Content               string     `json:"content"`
+	EvidenceURLS          []string   `json:"evidence_urls"`
+	OwnerAdjustmentReason string     `json:"owner_adjustment_reason"`
+	OwnerAdjustedAt       *time.Time `json:"owner_adjusted_at"`
+	RenterConfirmedAt     *time.Time `json:"renter_confirmed_at"`
+	RenterRejectedAt      *time.Time `json:"renter_rejected_at"`
+	CreatedAt             time.Time  `json:"created_at"`
+	UpdatedAt             time.Time  `json:"updated_at"`
+}