fix: use design system CodeBlock for error stack trace

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/ExecutionDiagram/tabs/ErrorTab.tsx

@@ -1,3 +1,4 @@
+import { CodeBlock } from '@cameleer/design-system';
 import type { ProcessorNode, ExecutionDetail } from '../types';
 import styles from '../ExecutionDiagram.module.css';
 
@@ -37,7 +38,7 @@ export function ErrorTab({ processor, executionDetail }: ErrorTabProps) {
       {errorStackTrace && (
         <>
           <div className={styles.errorStackLabel}>Stack Trace</div>
-          <pre className={styles.errorStackTrace}>{errorStackTrace}</pre>
+          <CodeBlock content={errorStackTrace} copyable />
         </>
       )}
     </div>