Update CHANGES.md for 0.8.0 release

## Description
`CHANGES.md` stops at 0.7.0. Needs an entry documenting the modernization work in 0.8.0.

## Acceptance Criteria
- [ ] 0.8.0 entry added covering Ruby 3.1+ requirement, Rails 6.1-7.1 support, PaperTrail 12+/15+
- [ ] Documents breaking changes (dropped Ruby 2.x, Rails 4/5, PaperTrail 3-10)
- [ ] Documents dependency updates (factory_bot, button_to, etc.)