feat: harden and relaunch the open-source skill

[hyt315]

Summary

• rebuild the landing page around responsible contribution outcomes, examples, installation and downloads
• fix Codex installation and make public reconnaissance credential-free
• strengthen repository-rule discovery, authorship, AI disclosure and external-write approval
• remove fake security contact, unsafe history-rewrite recipe, arbitrary PR size rules and stale tool assumptions
• add three inspectable workflows, CI, validator, social preview and repository metadata
• prepare v1.1.0

Validation

• local validator passed
• YAML parse passed
• privacy and Git-history credential scans passed
• clean-clone validation passed

Merge

Use rebase merge to preserve the verified Codex author identity.