Exclude the core/runtime/v2/README.md symlink in the links workflow so
lychee does not fail resolving relative links from the symlink path.
docs/runtime-v2.md is already validated directly.
Update broken, moved, and rate-limited links across markdown documents:
- Replace moved Kubernetes cgroup driver and GCP registry docs.
- Replace retired RHEL 6 devmapper docs with kernel.org reference.
- Point NSSM, CRIU, and Ansible references to GitHub repositories.
- Fix relative paths in remote-snapshotter.md and root-relative paths.
Assisted-by: Antigravity
Signed-off-by: Samuel Karp <samuelkarp@google.com>