fix(trading): 修复卖出预估计算，加入销毁倍数

卖出预估计算现在使用与后端一致的公式：
- 有效积分股 = 卖出量 × (1 + burnMultiplier)
- 卖出交易额 = 有效积分股 × 价格 × 0.9

修复的位置：
1. _calculateEstimate() 方法 - 预计获得显示
2. _handleTrade() 确认弹窗 - 显示销毁倍数和有效积分股明细

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mining-app/lib/presentation/pages/trading/trading_page.dart

@@ -810,21 +810,32 @@ class _TradingPageState extends ConsumerState<TradingPage> {
     );
   }
 
+  /// 计算预估获得/支出
+  /// 卖出公式：卖出交易额 = (卖出量 + 卖出销毁量) × 价格 × 0.9
+  ///         = 卖出量 × (1 + burnMultiplier) × 价格 × 0.9
   String _calculateEstimate() {
     final price = double.tryParse(_priceController.text) ?? 0;
     final quantity = double.tryParse(_quantityController.text) ?? 0;
-    final total = price * quantity;
 
-    if (total == 0) {
+    if (price == 0 || quantity == 0) {
       return '0.00 积分值';
     }
 
     if (_selectedTab == 1) {
-      // 卖出时扣除10%销毁
-      final afterBurn = total * 0.9;
-      return '${formatAmount(afterBurn.toString())} 积分值';
+      // 卖出时：有效积分股 = 卖出量 × (1 + burnMultiplier)
+      // 卖出交易额 = 有效积分股 × 价格 × 0.9（扣除10%手续费）
+      final marketAsync = ref.read(marketOverviewProvider);
+      final burnMultiplier = double.tryParse(
+        marketAsync.valueOrNull?.burnMultiplier ?? '0',
+      ) ?? 0;
+      final effectiveQuantity = quantity * (1 + burnMultiplier);
+      final grossAmount = effectiveQuantity * price;
+      final netAmount = grossAmount * 0.9; // 扣除10%手续费
+      return '${formatAmount(netAmount.toString())} 积分值';
     }
 
+    // 买入时：支出 = 价格 × 数量
+    final total = price * quantity;
     return '${formatAmount(total.toString())} 积分值';
   }
 
@@ -1036,9 +1047,20 @@ class _TradingPageState extends ConsumerState<TradingPage> {
 
     // 卖出时显示确认弹窗
     if (!isBuy) {
-      final total = price * quantity;
-      final burned = total * 0.1;
-      final received = total * 0.9;
+      // 获取销毁倍数，使用与后端一致的公式计算
+      final marketAsync = ref.read(marketOverviewProvider);
+      final burnMultiplier = double.tryParse(
+        marketAsync.valueOrNull?.burnMultiplier ?? '0',
+      ) ?? 0;
+
+      // 有效积分股 = 卖出量 × (1 + burnMultiplier)
+      final effectiveQuantity = quantity * (1 + burnMultiplier);
+      // 交易总额 = 有效积分股 × 价格
+      final grossAmount = effectiveQuantity * price;
+      // 手续费 = 交易总额 × 10%
+      final tradeFee = grossAmount * 0.1;
+      // 实际获得 = 交易总额 × 90%
+      final received = grossAmount * 0.9;
 
       final confirmed = await showDialog<bool>(
         context: context,
@@ -1052,10 +1074,14 @@ class _TradingPageState extends ConsumerState<TradingPage> {
               const SizedBox(height: 8),
               Text('卖出价格: ${formatPrice(price.toString())} 积分值'),
               const SizedBox(height: 8),
-              Text('交易总额: ${formatAmount(total.toString())} 积分值'),
+              Text('销毁倍数: ${burnMultiplier.toStringAsFixed(4)}'),
+              const SizedBox(height: 8),
+              Text('有效积分股: ${formatAmount(effectiveQuantity.toString())}'),
+              const SizedBox(height: 8),
+              Text('交易总额: ${formatAmount(grossAmount.toString())} 积分值'),
               const SizedBox(height: 8),
               Text(
-                '进入积分股池: ${formatAmount(burned.toString())} 积分值 (10%)',
+                '进入积分股池: ${formatAmount(tradeFee.toString())} 积分值 (10%)',
                 style: const TextStyle(color: _green),
               ),
               const SizedBox(height: 8),