- Add Appraisal gem for managing multiple test gemfiles
- Create test matrix for Rails 6.1-8.0 and ActiveAdmin 2.9-4.x
- Consolidate multiple workflow files into single ci.yml
- Use matrix strategy to test across Ruby 3.0-3.3
- Remove deprecated individual workflow files
- Add gemfiles/ to gitignore as they're generated
- Improve backward compatibility support