SiYuan: Incomplete Fix Bypass for CVE-2026-30869: Path Traversal via Double URL Encoding in `/export/` Endpoint

SiYuan is an open-source personal knowledge management system. Prior to 3.6.5, the fix for CVE-2026-30869 only added a denylist check (IsSensitivePath) but did not address the root cause — a redundant url.PathUnescape() call in serveExport(). An authenticated attacker can use double URL encoding (%252e%252e) to traverse directories and read arbitrary workspace files including the full SQLite database (siyuan.db), kernel log, and all user documents. This vulnerability is fixed in 3.6.5.