Integrate pyrefly static type checker into the development workflow
  with both local make targets and CI automation.

  Changes:
  - Add pyrefly>=0.1.0 to dev dependency group in pyproject.toml
  - Add 'make typecheck' target to run pyrefly check --summarize-errors
  - Integrate 'pyrefly init' into 'make setup' workflow
  - Create GitHub Actions workflow for automated type checking on PRs
  - Update Makefile help text to include type checking commands

  The pyrefly configuration in pyproject.toml excludes common non-code
  directories (node_modules, __pycache__, venv)