Add GitHub Actions workflow for documentation deployment

[Copilot]

Adds missing GitHub Actions workflow to automate documentation deployment to GitHub Pages.

Changes

• .github/workflows/docs.yml: Workflow to build and deploy MkDocs documentation on push to main or manual trigger
  • Uses Python 3.10, uv, and mkdocs with Material theme
  • Deploys to GitHub Pages via mkdocs gh-deploy

Context

The documentation infrastructure (mkdocs.yml, docs/, Makefile targets) was added in PR #124 but the workflow file couldn't be created by the GitHub App due to permissions. This PR completes the documentation setup.

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[coderabbitai]

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch copilot/sub-pr-128

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[sonarqubecloud]

Quality Gate failed

Failed conditions
1 Security Hotspot

See analysis details on SonarQube Cloud