curl --request GET \
  --url https://zeus-api.agentspro.cn/api/knowledge-base/kb_abc123/documents/doc_xyz789/content \
  --header 'Authorization: Bearer <token>'

{
  "content": "# Product User Guide\n\n## 1. Installation\n\nDownload the installer package...",
  "fileName": "product-guide.md",
  "fileType": "text/markdown"
}