fix: 消除 code-block-body 背景色与 shiki 主题背景色视觉割裂

src/web/features/chat/parts/CodeBlock.tsx

@@ -63,9 +63,11 @@ export function CodeBlock({ children, className: _className, isStreaming }: Code
       {highlighted ? (
         <div className="code-block-body" dangerouslySetInnerHTML={{ __html: highlighted }} />
       ) : (
-        <pre className="code-block-body">
-          <code>{codeText}</code>
-        </pre>
+        <div className="code-block-body">
+          <pre>
+            <code>{codeText}</code>
+          </pre>
+        </div>
       )}
     </div>
   );