fix(mining-app): C2C"我的"列表待接单订单增加取消按钮

在我的订单卡片上直接显示取消按钮（PENDING状态），
弹出确认对话框后调用 cancelOrder API

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

frontend/mining-app/lib/presentation/pages/c2c/c2c_market_page.dart

@@ -509,10 +509,30 @@ class _C2cMarketPageState extends ConsumerState<C2cMarketPage>
               ],
             ),
             const SizedBox(height: 8),
-            // 时间
-            Text(
-              '创建于 ${_formatDateTime(order.createdAt)}',
-              style: TextStyle(fontSize: 12, color: AppColors.textSecondaryOf(context)),
+            // 时间 + 操作按钮
+            Row(
+              mainAxisAlignment: MainAxisAlignment.spaceBetween,
+              children: [
+                Text(
+                  '创建于 ${_formatDateTime(order.createdAt)}',
+                  style: TextStyle(fontSize: 12, color: AppColors.textSecondaryOf(context)),
+                ),
+                if (order.status == C2cOrderStatus.pending)
+                  GestureDetector(
+                    onTap: () => _handleCancelOrder(order),
+                    child: Container(
+                      padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 4),
+                      decoration: BoxDecoration(
+                        border: Border.all(color: _red.withOpacity(0.5)),
+                        borderRadius: BorderRadius.circular(4),
+                      ),
+                      child: Text(
+                        '取消',
+                        style: TextStyle(fontSize: 12, color: _red),
+                      ),
+                    ),
+                  ),
+              ],
             ),
           ],
         ),
@@ -962,6 +982,45 @@ class _C2cMarketPageState extends ConsumerState<C2cMarketPage>
     );
   }
 
+  Future<void> _handleCancelOrder(C2cOrderModel order) async {
+    final confirmed = await showDialog<bool>(
+      context: context,
+      builder: (ctx) => AlertDialog(
+        title: const Text('确认取消'),
+        content: const Text('确定要取消此订单吗？'),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(ctx, false),
+            child: const Text('暂不'),
+          ),
+          TextButton(
+            onPressed: () => Navigator.pop(ctx, true),
+            child: Text('确认取消', style: TextStyle(color: _red)),
+          ),
+        ],
+      ),
+    );
+    if (confirmed != true) return;
+
+    final notifier = ref.read(c2cTradingNotifierProvider.notifier);
+    final success = await notifier.cancelOrder(order.orderNo);
+
+    if (success && mounted) {
+      ref.invalidate(myC2cOrdersProvider);
+      ScaffoldMessenger.of(context).showSnackBar(
+        const SnackBar(content: Text('订单已取消'), backgroundColor: _green),
+      );
+    } else if (mounted) {
+      final error = ref.read(c2cTradingNotifierProvider).error;
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(
+          content: Text('取消失败: ${error ?? '未知错误'}'),
+          backgroundColor: _red,
+        ),
+      );
+    }
+  }
+
   Future<void> _takeOrder(
     C2cOrderModel order, {
     String? quantity,