docs: update stale contribution link and security contact

The repository's CONTRIBUTING.md still links contributors to the legacy claude-flow/issues path, while the project is now ruflo. SECURITY.md gives two different contact domains: reporting uses security@cognitum.one but policy questions use security@ruv.io. This is confusing and can route contributors or security researchers to the wrong destination. Proposed fix: point CONTRIBUTING.md at ruvnet/ruflo/issues and use security@cognitum.one consistently.

Update CONTRIBUTING.md so the issue link points to ruvnet/ruflo/issues, then inspect SECURITY.md and make both security contacts use security@cognitum.one. Review both files for the two stale references and confirm the links and email addresses are consistent when done.

Written by the indexing model from the issue text.