fix: improve import, evidence indexing and material-scoped grading

Preserve document revisions and evidence, harden indexing and export behavior, add explicit material selection and direct-folder import, validate model JSON schemas with safe error messages, and retain student selection while loading scoring data.

frontend/src/Chat.tsx

@@ -112,7 +112,9 @@ function CitationCards({ items }: { items: any[] }) {
     const sourceHref = safeUrl(item.url);
     const scoreHref = safeUrl(item.score_url);
     const imageHref = safeUrl(item.image_url);
-    return <div className="citation-card" key={`${name}-${page}-${index}`}><div className="citation-heading"><Text strong>{name}</Text>{place && <Tag>{place}</Tag>}</div>
+    return <div className="citation-card" key={`${name}-${page}-${index}`}><div className="citation-heading"><Text strong>{name}</Text>{place && <Tag>{place}</Tag>}
+      {item.page_type_label && <Tag color={['body', 'appendix'].includes(item.page_type) ? 'green' : 'orange'}>{item.page_type_label}</Tag>}
+      {item.source_role === 'structure' && <Tag>结构信息</Tag>}{item.historical && <Tag>历史评分引用</Tag>}</div>
       {quote && (quote.length > 320 ? <details><summary>{quote.slice(0, 240)}… 展开原文</summary><p>{quote}</p></details> : <p>{quote}</p>)}
       <Space wrap size="small">{sourceHref && <a href={sourceHref} target="_blank" rel="noopener noreferrer">{sourceLabel(sourceHref)}</a>}
         {scoreHref && scoreHref !== sourceHref && <a href={scoreHref} target="_blank" rel="noopener noreferrer">查看评分</a>}