支持结账多轮协商与按实际消耗双比例结算

允许双方最多 6 轮修改结账方案；哈夫币按实际消耗与 buyer/seller 比例计价，打超从押金扣，押金不足禁止自动完结并引导人工争议。同步收紧结账明细展示密度。

frontend/src/features/orders/api/orders.ts

@@ -70,6 +70,12 @@ export interface Checkout {
   order_id: number
   initiated_by: number
   status: SettlementStatus
+  round_count?: number
+  turn?: 'owner' | 'renter' | string
+  proposed_by?: number
+  max_rounds?: number
+  can_counter?: boolean
+  can_accept?: boolean
   price_role?: 'renter' | 'owner' | 'admin' | string
   display_amount_cent: number
   rent_amount_cent?: number
@@ -82,6 +88,8 @@ export interface Checkout {
   deposit_deduct_amount_cent: number
   renter_refund_amount_cent?: number
   owner_income_amount_cent?: number
+  shortfall_cent?: number
+  overshoot_amount_cent?: number
   content: string
   evidence_urls: string[]
   owner_adjustment_reason: string