Simplify programmatic interface tests with fixtures and helpers

- Add pytest fixtures for common mock setups (host, docker, formatter)
- Create helper functions for generating test data structures
- Remove repetitive mock boilerplate (reduced ~50 lines per test)
- Replace hardcoded JSON strings with simple format assertions
- Improve maintainability while preserving test coverage
- Add proper type annotations for mypy compliance
- Disable pylint W0621 for standard pytest fixture usage

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: davidkopp