BUG修复，返回结构统一

client/src/components/CodePreview.vue

@@ -358,7 +358,13 @@ const runCode = async () => {
         })
       })
       
-      const result = await response.json()
+      if (!response.ok) {
+        const errorData = await response.json()
+        throw new Error(errorData.message || '代码执行失败')
+      }
+      
+      const data = await response.json()
+      const result = data.result // 从统一响应格式中提取 result
       
       let outputHtml = ''
       if (result.error) {