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/composables/useOrderSnapshot.ts

@@ -35,9 +35,10 @@ export function useOrderCheckoutSnapshot(options: {
     calculateResourceChargeAmount(checkoutResources.value, options.resourceUsage.value)
   )
   const snapshotHafCoinM = computed(() => getSnapshotHafCoinM(options.order.value))
+  // 允许为负：表示打超（实际消耗 > 发布量）
   const remainingHafCoinM = computed(() =>
     roundQuantity(
-      Math.max(snapshotHafCoinM.value - Number(options.checkoutForm.value.coin_consumed_m || 0), 0)
+      snapshotHafCoinM.value - Number(options.checkoutForm.value.coin_consumed_m || 0)
     )
   )
 
@@ -167,11 +168,14 @@ export function buildCheckoutContentWithSummary(options: {
     )
   }
   if (Number(options.coinConsumedM || 0) > 0) {
-    lines.push(
-      `哈夫币消耗：${quantity(options.coinConsumedM)}M，预计剩余${quantity(
-        options.remainingHafCoinM
-      )}M`
-    )
+    const remain = Number(options.remainingHafCoinM || 0)
+    if (remain >= 0) {
+      lines.push(`哈夫币实际消耗：${quantity(options.coinConsumedM)}M，预计剩余${quantity(remain)}M`)
+    } else {
+      lines.push(
+        `哈夫币实际消耗：${quantity(options.coinConsumedM)}M，打超${quantity(-remain)}M（超额按比例从押金结算）`
+      )
+    }
   }
   if (lines.length === 0) {
     lines.push('租客发起结账。')