CVE-2026-83619: xmldom: End-tag Whitespace-Trim Regex ReDoS — quadratic backtracking in the 0.8.x end-tag parser

On the @xmldom/xmldom 0.8.x line, parsing an XML end tag whose name is followed by a long run of whitespace and then a non-whitespace character triggers quadratic-time regular-expression backtracking (ReDoS), so a single small crafted end tag stalls the Node.js event loop. It is reachable from DOMParser.parseFromString under default options, unauthenticated, before any validity check — an availability-only denial of service. The 0.9.x line is not affected.