复盘统计改为分色堆叠柱状图，替代节点树图。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/ExamReviewPanel.tsx

@@ -3,7 +3,7 @@ import { useEffect, useMemo, useState } from 'react'
 import { examApi } from '../api/client'
 import type { Exam, ReviewStatus } from '../types'
 import { EXAM_TYPE_LABELS, REVIEW_STATUS_OPTIONS } from '../types'
-import ReviewTreeChart from './ReviewTreeChart'
+import ReviewBarChart from './ReviewBarChart'
 
 function apiErrorMessage(err: unknown, fallback: string): string {
   if (err && typeof err === 'object' && 'response' in err) {
@@ -147,7 +147,7 @@ export default function ExamReviewPanel({ exams, onRefresh }: Props) {
                 </>
               )}
               <Typography.Text strong>复盘统计</Typography.Text>
-              <ReviewTreeChart exams={exams} />
+              <ReviewBarChart exams={exams} />
             </Space>
           ),
         },