Migrate GitHub Pages deployment to official actions

Current State

This repository currently uses JamesIves/github-pages-deploy-action@releases/v3 for deploying documentation to GitHub Pages (as seen in .github/workflows/push.yaml).

Proposed Change

Migrate to the official GitHub Actions for Pages deployment:

• actions/configure-pages@v5
• actions/upload-pages-artifact@v3
• actions/deploy-pages@v4

Benefits

• Official GitHub support and maintenance
• Better integration with GitHub Pages settings
• Follows GitHub's recommended best practices
• More reliable and secure

Implementation

Follow the official guide: https://docs.github.com/en/pages/getting-started-with-github-pages/using-custom-workflows-with-github-pages

Example implementation: https://github.com/MaxGhenis/disutility-of-uncertainty/pull/2

Required Changes

1. Add proper permissions to workflow:

permissions:
  contents: read
  pages: write
  id-token: write

2. Update deployment steps to use official actions
3. Change GitHub Pages source to "GitHub Actions" in repository settings

This would modernize the deployment pipeline and align with GitHub's current recommendations.

Start with .github/workflows/push.yaml and the linked official GitHub Pages guide. Replace the existing deployment action with the specified Pages actions and permissions, then change the repository Pages source to GitHub Actions; done means the documentation deployment succeeds through the new workflow.