Apply immediately changes in model/prompt/mode without any further steps

[apalazzi]

Not sure if it's eca-emacs or eca, anyway I think that changes in model/agent/variant/whatever should be applied immediately to the chat: after all, if I change something at a certain point in the chat is because I estimated it's time to change something: no need to do further steps, maybe add an option to ask confirmation or just apply changes.

[ericdallo]

@apalazzi currently we change on next user prompt because there is a ongoing loop in the server, we could offer that but would require some refactor in server side that I don't know it's worth it