CVE-2026-6968: Multiple Path Traversal Variants in awslabs/tough

Incomplete path traversal fixes in awslabs/tough before tough-v0.22.0 allow remote authenticated users with delegated signing authority to write files outside intended output directories via absolute target names in copy_target/link_target, symlinked parent directories in save_target, or symlinked metadata filenames in SignedRole::write, because write paths trust the joined destination path without post-resolution containment verification. We recommend you upgrade to tough-v0.22.0 / tuftool-v0.15.0.