Add repository governance, contribution handbook, templates, and docs-quality CI

[csecrestjr]

Motivation

• Establish a baseline governance and contributor experience for the NTARI Developer Portal with community health files, contribution guidance, and ownership placeholders.
• Provide a production-ready, Markdown-first engineering handbook to capture COSDS processes and expectations.
• Prevent common repo hygiene issues and improve documentation quality via editor, ignore, and CI/link/spellcheck automation.

Description

• Added community and governance files: README.md updates, CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md, CODEOWNERS, and a REPOSITORY_READINESS_REPORT.md.
• Added structured issue forms in .github/ISSUE_TEMPLATE/ (bug_report.yml, feature_request.yml, documentation_improvement.yml, engineering_rfc.yml) and a pull request template at .github/PULL_REQUEST_TEMPLATE.md.
• Added repository housekeeping files: .editorconfig and .gitignore.
• Added CI workflows to improve docs quality: markdown-lint.yml (uses markdownlint-cli2), broken-link-check.yml (uses lychee-action), and spellcheck.yml (uses codespell).
• Added a comprehensive docs/engineering-handbook/ with many handbook chapters (purpose, principles, workflow, review standards, security, CI/CD, release management, onboarding checklists, etc.) and supporting checklist and onboarding pages.

Testing

• No automated tests were executed as part of this change in the rollout; the change only adds files and CI workflows.
• The added GitHub Actions workflows will run on future pushes or pull requests and are configured to run markdownlint-cli2, lychee link checks, and codespell as the automated quality gates.
• Manual inspection was used to author and format the YAML and Markdown files prior to submission.

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Codex Task