Initial repository governance, engineering handbook, and documentation CI workflows

[csecrestjr]

Motivation

• Establish a baseline open-source governance and contributor experience for the NTARI Developer Portal.
• Provide a minimal, Markdown-first Engineering Handbook skeleton to capture future policies and process guidance.
• Add GitHub-native intake and review scaffolding so contributors have clear templates and maintainers can enforce ownership.
• Introduce lightweight quality gates for Markdown via GitHub Actions to catch link, lint, and spelling issues early.

Description

• Added repository governance and community files including CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md, CODEOWNERS, README.md, and a REPOSITORY_READINESS_REPORT.md.
• Added GitHub Issue Forms and a pull request template under .github/ISSUE_TEMPLATE/ and .github/PULL_REQUEST_TEMPLATE.md to standardize issue and PR submission.
• Created GitHub Actions workflows for markdown-lint, broken-link-check, and spellcheck at .github/workflows/ and configured them to run on pull_request and push for Markdown changes.
• Added an .editorconfig, .gitignore, and SECURITY.md, plus a broad set of docs/engineering-handbook/ placeholder chapters to capture future handbook content.

Testing

• No automated CI runs were executed as part of this change; the new workflows are configured to trigger on pull_request and push and will run on subsequent events.
• The change adds markdownlint-cli2, lychee-action, and codespell steps in workflows so future PRs will run Markdown linting, broken-link checks, and spellchecking respectively.
• All YAML and Markdown files were added in a focused manner to avoid introducing runtime code, minimizing risk for CI failures on first runs.
• Repository readiness guidance (REPOSITORY_READINESS_REPORT.md) documents recommended follow-up validations and workflow tuning after initial CI runs.

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Codex Task