[jigar-dhulla]

The API only returns a relationship when the request names it in include (same cause as #276). domain:get and domain:list never asked for environment, so environmentId was always null. Domains now request it by default, and a test covers both get and list.

Related to #279. This fixes environmentId only. environment:get already requests primaryDomain by default, and domains is not in the environment endpoint's documented include values, so domainIds is still empty. That part needs the API to allow include=domains, or the CLI to fill it from the domain list.

[jigar-dhulla]

I checked this against the live API with real calls (read-only, one domain attached to one environment). The include=environment in this PR is what makes the link appear:

Request	Result
GET /domains/{id}	200, relationships empty
GET /domains/{id}?include=environment	200, relationships.environment points at the environment, and included has the environment
GET /environments/{id}/domains	200, no environment relationship
GET /environments/{id}/domains?include=environment	200, relationships.environment present

So environmentId stays null today only because the request does not ask for it.