Add development environment readiness stage

[rochecompaan]

Summary

• add optional skills.developmentEnvironment stage before implementation
• return development-environment-not-ready with evidence/remediation when local prep cannot complete
• pass successful prep to implementation as untrusted JSON handoff data
• document the new skill, workflow stage, and result contract
• split readiness parsing/stage logic into focused helpers and tests

Verification

• npm run lint
• npm test (805 pass / 0 fail)