Add GitHub Actions Workflow Files

[jtdub]

Problem

The README and CHANGELOG reference CI/CD workflows but no .github/workflows/ directory exists in the repository.

Proposed Solution

Create GitHub Actions workflows for:

1. Test Workflow

• Run on PRs and pushes to main
• Test on Python 3.10, 3.11, 3.12, 3.13
• Upload coverage reports

2. Lint Workflow

• Run Black, Ruff, Mypy checks

3. Release Workflow

• Build and publish to PyPI on release

4. Documentation Workflow

• Build and deploy MkDocs to GitHub Pages

Acceptance Criteria

• Test workflow runs on PRs and pushes
• Tests run on all supported Python versions
• Lint workflow checks Black, Ruff, Mypy
• Release workflow publishes to PyPI
• Documentation workflow deploys to GitHub Pages
• All badges in README work correctly