Add Codex project Skills

[bluecoast1379]

Summary

• replace unsupported project-level Codex prompts with one umbrella Skill and 32 manifest-driven stage Skills
• add conservative 0.1.0 migration that preserves custom files, workspace facts, same-name Skills, nested backups, and symlink boundaries
• release as 1.0.0 with conformance, migration, packaging, and publication evidence checks

Verification

• npm run check
• private denylist scan
• Codex app-server skills/list: 33 enabled repo Skills, zero errors
• npm run build:release
• two independent final reviews with no remaining findings