Windmill and Centrifugo in production

The full-setup windmill-dev and centrifugo-dev apps are local-dev stand-ins for the production NixOS services. For a production deployment, the module at core/components/hosting-provider/windmill/windmill.nix deploys Windmill, and services.fediversity-api.centrifugo.enable in nix/centrifugo.nix deploys Centrifugo, with an nginx virtual host on centrifugo.domain. The front-end gives the base URL of its proxy views in centrifugo.proxyBaseUrl.