📝 docs(contributing): create comprehensive development guide

Added CONTRIBUTING.md with complete development documentation:

✨ Sections:
- Development setup (local and Docker)
- Testing guide (pytest commands, test structure, coverage)
- Test coverage breakdown (142 tests, 75.37% coverage)
- Micro-commit philosophy and glassbear format
- Pull request workflow
- Coverage requirements for contributors
- Debugging tips and common issues
- Performance testing guidelines

This consolidates testing and development docs from README,
making it easier for contributors to get started.

Coverage details include:
- 142 unit and integration tests
- 75.37% overall coverage (exceeds 75% target)
- Detailed breakdown by module
- Codecov integration documentation

🤖 Generated with Claude Code

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

Author: christopher-igweze