Add GitHub Actions workflow for CI/CD

[moshesham]

Problem

No automated CI/CD pipeline exists. Code quality issues may be merged without detection.

Missing Automation

• Running tests on PR
• Linting code
• Type checking
• Security scanning
• Coverage reporting

Impact

• Code quality issues may be merged
• No automated testing before merge
• Manual review burden on maintainers
• Inconsistent code quality

Tasks

• Create .github/workflows/ci.yml
• Add lint job (flake8, black, isort, mypy)
• Add test job with matrix for Python 3.10, 3.11, 3.12
• Add security scan job (bandit, safety)
• Configure codecov for coverage reporting
• Add status badges to README.md
• Test workflow with a PR
• Document CI/CD process in CONTRIBUTING.md

References

• PROJECT_REVIEW.md Issue Add complete type hints to all public methods and functions #13
• PRODUCT_ROADMAP.md TASK-014