作业帮式错题标注：OCR 定位错误红框 + 解题思路。

- PaddleOCR 行级坐标 + AI 识别错答区域，生成标注图

- 解法拆分为「解题思路」与「详细解答」

- 详情页标注图/原图切换，列表显示标注缩略图

frontend/src/components/AuthenticatedImage.tsx

@@ -3,6 +3,7 @@ import api from '../api/client'
 
 interface Props {
   questionId: string
+  variant?: 'original' | 'annotated'
   className?: string
   alt?: string
   style?: React.CSSProperties
@@ -10,6 +11,7 @@ interface Props {
 
 export default function AuthenticatedImage({
   questionId,
+  variant = 'original',
   className,
   alt = '题目',
   style,
@@ -21,36 +23,58 @@ export default function AuthenticatedImage({
     let objectUrl: string | null = null
     let cancelled = false
 
-    api
-      .get(`/wrong-questions/${questionId}/image`, { responseType: 'blob' })
-      .then((res) => {
+    const load = async (path: string, fallback?: string) => {
+      try {
+        const res = await api.get(path, { responseType: 'blob' })
         if (cancelled) return
         objectUrl = URL.createObjectURL(res.data)
         setSrc(objectUrl)
         setFailed(false)
-      })
-      .catch(() => {
-        if (!cancelled) setFailed(true)
-      })
+      } catch {
+        if (fallback && !cancelled) {
+          await load(fallback)
+        } else if (!cancelled) {
+          setFailed(true)
+        }
+      }
+    }
+
+    const annotatedPath = `/wrong-questions/${questionId}/annotated-image`
+    const originalPath = `/wrong-questions/${questionId}/image`
+
+    if (variant === 'annotated') {
+      load(annotatedPath, originalPath)
+    } else {
+      load(originalPath)
+    }
 
     return () => {
       cancelled = true
       if (objectUrl) URL.revokeObjectURL(objectUrl)
     }
-  }, [questionId])
+  }, [questionId, variant])
 
   if (failed) {
     return (
-      <div className={className} style={{ ...style, background: '#fafafa', color: '#999', display: 'flex', alignItems: 'center', justifyContent: 'center', fontSize: 12 }}>
+      <div
+        className={className}
+        style={{
+          ...style,
+          background: '#fafafa',
+          color: '#999',
+          display: 'flex',
+          alignItems: 'center',
+          justifyContent: 'center',
+          fontSize: 12,
+        }}
+      >
         图片加载失败
       </div>
     )
   }
 
   if (!src) {
-    return (
-      <div className={className} style={{ ...style, background: '#fafafa' }} />
-    )
+    return <div className={className} style={{ ...style, background: '#fafafa' }} />
   }
 
   return <img src={src} alt={alt} className={className} style={style} />

frontend/src/components/WrongQuestionList.tsx

@@ -38,7 +38,7 @@ export default function WrongQuestionList({
         {items.map((wq) => (
           <div key={wq.id} className="wq-card">
             <div className="wq-card-click" onClick={() => onSelect(wq.id)}>
-              <AuthenticatedImage questionId={wq.id} alt="题目" className="wq-card-img" />
+              <AuthenticatedImage questionId={wq.id} variant="annotated" alt="题目" className="wq-card-img" />
               <div className="wq-card-body">
                 <Typography.Text strong>{wq.subject_name}</Typography.Text>
                 {wq.category === 'olympiad' && (