[codex] improve OSS readiness

[davidweb3-ctrl]

Summary

• Reposition README around open-source maintainer workflows for Codex for OSS.
• Add SECURITY, ROADMAP, and Codex for OSS maintenance planning docs.
• Add issue templates, PR template, and CODEOWNERS.
• Strengthen CI to run lint, formatting, tests, build, and an MCP smoke test.
• Fix the placeholder test to use Jest consistently, update package metadata, clean release packaging, and resolve dependency audit findings.

Validation

• npm run lint
• npm run format:check
• npm test: 44 passed
• npm run build
• npm audit: 0 vulnerabilities
• npm pack --dry-run
• MCP initialize smoke test

Notes

This PR does not change or delete the existing remote release/tag. The current nonstandard #MCP release tag should be cleaned up separately after review.