Release v0.3.1

Code quality improvements and RuboCop compliance fixes:
- Comprehensive style and complexity improvements
- Enhanced maintainability through method refactoring
- Added class documentation
- Fixed Nix packaging issues

This release focuses on improving code quality and maintainability
while preserving all existing functionality.

chore: bump version to 0.3.0

- Update version in lib/hubctl/version.rb, hubctl.gemspec, and flake.nix
- Add comprehensive changelog entry for v0.3.0 featuring:
  - Username support for organization invitations
  - Direct team member invitations without prior org membership
  - Enhanced error handling and API compatibility
- This release includes new functionality so warrants a minor version bump

chore: bump version to v0.2.1

- Fix Nix build compatibility issues
- Resolve gem dependency hashing problems
- Improve build reproducibility across environments
- Update version references in all project files
- Add v0.2.1 changelog entry with technical details

docs: release v0.2.0 with comprehensive enterprise features

- Create CHANGELOG.md with detailed version history following Keep a Changelog format
- Update version to 0.2.0 across all files (version.rb, gemspec, flake.nix)
- Enhanced README.md with comprehensive enterprise management documentation
- Added detailed enterprise billing analytics examples with JSON output
- Documented SAML SSO management, security settings, and audit log access
- Updated gemspec description to highlight enterprise capabilities
- Updated flake.nix description and version for Nix users
- Replaced inline changelog with reference to CHANGELOG.md file

New enterprise features include:
- Billing insights with cost breakdowns by service and runner type
- Member and owner management with role-based access control
- Organization creation and management within enterprises
- SAML SSO authorization lifecycle management
- Security analysis settings configuration
- Comprehensive audit log access with filtering
- Multi-format output support (JSON, table, list) for all commands