Fix: Use DOMPurify to filter out dangerous HTML #7668 (#7669)

### What problem does this PR solve?

Fix: Use DOMPurify to filter out dangerous HTML #7668

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

web/src/pages/chat/markdown-content/index.tsx

   const { setDocumentIds, data: fileThumbnails } =
     useFetchDocumentThumbnailsByIds();
   const contentWithCursor = useMemo(() => {
-    let text = content;
+    let text = DOMPurify.sanitize(content);
     if (text === '') {
       text = t('chat.searching');
     }