Renovate outdated cf-pages.yml GitHub Action workflow

[Copilot]

The cf-pages.yml workflow was created about 3 years ago and contained several outdated components. This PR brings it up to modern GitHub Actions standards by aligning it with the patterns used in the newly created build-html.yml workflow.

Changes Made

Updated GitHub Actions versions:

• actions/checkout@v3 → actions/checkout@v4
• actions/setup-node@v3 → actions/setup-node@v4

Updated runtime environment:

• ubuntu-20.04 → ubuntu-latest
• Node.js version 16 → 18

Improved step naming:

• Added descriptive names to all workflow steps following modern conventions
• run: npm install → - name: Install dependencies
• run: npm run build-site → - name: Build site

What Was Preserved

As requested, the Cloudflare Pages deployment section was left untouched:

• cloudflare/pages-action@v1 usage maintained
• All secrets and configuration preserved
• Directory structure and deployment settings unchanged

Verification

• ✅ Build process tested locally with Node.js 18
• ✅ Output directory structure remains compatible with Cloudflare Pages
• ✅ No breaking changes to existing deployment workflow
• ✅ All modernizations follow current GitHub Actions best practices

The workflow is now aligned with modern standards while maintaining full backward compatibility with the existing Cloudflare Pages deployment.

Fixes #15.

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