- support upsert in AddEnvironment, no-op RemoveEnvironment if absent
- fallback active env to devnet on remove, add tests
- integrate with sandbox create/destroy, ignore core/plans/
- add monorepo Makefile delegating to sub-projects
- update CI workflows, GoReleaser, gitignore for new structure
- revise README, CONTRIBUTING.md for monorepo overview
- bump Go to 1.24