lightrag-hku: SSRF via IPv6-transition address bypass (NAT64, IPv4-compatible, 6to4) of the native-markdown image-download guard

Summary LightRAG's native markdown parser downloads external images referenced by an uploaded markdown or textpack document. The only SSRF guard, validatedaddresses in lightrag/parser/markdown/parser.py, resolves the image host and rejects it when the resolved IP is not isglobal. That check is...