Create and manage Railway environments via the API, including cloning and ephemeral PR environments

Documented steps

1. Create: mutation environmentCreate with EnvironmentCreateInput { projectId, name, sourceEnvironmentId (optional), isEphemeral (optional) }
2. sourceEnvironmentId clones variables and settings from an existing environment into the new one
3. isEphemeral: true creates an ephemeral environment (used for PR previews); the environments query's isEphemeral filter set to false excludes them from listings
4. Rename with environmentRename (EnvironmentRenameInput); delete with environmentDelete; inspect with query environment / environments
5. Environment-scoped changes can be staged and committed via environmentStagedChanges (query) and environmentPatchCommitStaged (mutation)
6. Docs: https://docs.railway.com/guides/manage-environments