dev: Add Markdown lint setup and docs-analysis CI workflow

[offich]

Description

Add Markdown linting to the project using markdownlint-cli2, along with
a CI workflow (docs-analysis.yml) that runs the lint on push.

What was done

• Installed markdownlint-cli2 and configured pnpm as the package manager
• Added .markdownlint-cli2.yaml to disable line-length check in code blocks
• Fixed existing Markdown lint errors in CHANGELOG.md and
  docs/dev/review-guideline.md
• Added .github/workflows/docs-analysis.yml with:
  • Triggered on changes to .md files, package.json, pnpm-lock.yaml,
    and the workflow file itself
  • Uses jdx/mise-action (v4.0.1) for Node setup
  • Uses pnpm/action-setup (v5.0.0) to install pnpm
  • Caches pnpm store with actions/cache (v5.0.5)
  • Runs pnpm run lint:markdown
• Updated .gitignore to exclude node_modules

What was NOT done

• Lint rules other than line-length are left at default
• No auto-fix step in CI

Operation Confirmation

Steps

pnpm install
pnpm run lint:markdown

Related URLs

• https://github.com/DavidAnson/markdownlint-cli2
• https://github.com/jdx/mise-action
• https://github.com/pnpm/action-setup