Set Up Markdownlint CI Pipeline

A team uses a GitHub repository with Markdown documentation across multiple directories. There are currently no automated checks for documentation quality.

Set up a GitHub Actions CI workflow that runs markdownlint-cli2 on every pull request and push to main. The workflow must:

1. Run markdownlint-cli2 across all **/*.md files, excluding node_modules/.
2. Use Node.js 20 with npm caching.
3. Fail the build if any markdownlint errors are found.
4. Use a configuration file .markdownlint.json that:
   • Enables all rules by default.
   • Configures MD013 (line length) to 120 characters, excluding code blocks and tables.
   • Configures MD033 (inline HTML) to allow details, summary, br, and img.
   • Configures MD024 (no-duplicate-heading) to siblings_only: true.
5. Include a lint:md script in package.json that runs the linter.

Produce two files:

• .github/workflows/markdown-lint.yml — the CI workflow
• package.json — the root package.json with the lint script (only the relevant fields)