CVE-2026-45576: zrok copy writes attacker-controlled WebDAV paths outside the destination root

Alice runs zrok2 copy from a WebDAV or zrok drive controlled by Bob into a local filesystem target. Bob returns a DAV href such as /../outside.txt. The sync pipeline stores that path in the source inventory and passes it to FilesystemTarget.WriteStream, which joins it with the target root and creates the file outside Alice’s selected directory.