Initialize repository governance, templates, CI workflows, and handbook placeholders

[csecrestjr]

Motivation

• Establish a consistent repository foundation for the NTARI Developer Portal including contribution guidance, community standards, and formatting rules.
• Provide GitHub-native intake and review templates to standardize issues and pull requests.
• Add automated quality gates and placeholder handbook pages to prepare for future documentation growth.

Description

• Add governance and contributor files including CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md, CODEOWNERS, and REPOSITORY_READINESS_REPORT.md and update README.md for the NTARI Developer Portal.
• Introduce GitHub issue forms and a pull request template under .github/ISSUE_TEMPLATE/ and .github/PULL_REQUEST_TEMPLATE.md.
• Add CI workflows markdown-lint.yml, broken-link-check.yml, and spellcheck.yml under .github/workflows/ to lint Markdown, check links with lychee, and run codespell.
• Add editor and repository housekeeping files including .editorconfig, .gitignore, and a large set of placeholder handbook pages under docs/engineering-handbook/ to scaffold future content.

Testing

• No automated tests were executed as part of this change.
• Continuous integration workflows for Markdown linting, link checking, and spellchecking were added and are configured to run on pull_request and push to main.
• The new workflows use DavidAnson/markdownlint-cli2-action@v19, lycheeverse/lychee-action@v2, and codespell respectively and will report results on subsequent runs.

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Codex Task