Create a testing-and-qa registry

[varunreddy]

Summary

Add a registry focused on testing and QA practices: pytest patterns, property-based testing, load testing, contract testing, and test architecture.

Acceptance Criteria

• Create instruction files: pytest-patterns.md, property-based-testing.md, load-testing.md, contract-testing.md in examples/registry/instructions/
• Each file follows the 8-section template
• Create testing-qa.registry.yaml in examples/registry/
• Add all tools to tools.json and tools.yaml
• Create a qa-engineer role in examples/registry/roles/
• Test retrieval with relevant queries