Leave a project you were invited to

Remove YOURSELF from a project someone else shared with you. This is the one project call that names nobody but the caller: the only field is the project, so it can never remove another person, and it is the half of membership you can exercise on a project you did not create. Removing someone ELSE is removeMembers on PUT /projects/update, and only the project's creator can do that. Afterwards the project stops appearing in GET /projects/list and you can no longer read it. Getting back in needs a fresh invitation from the project's creator — there is no rejoin call — so confirm with the user before leaving on their behalf. Nothing else is touched. Jobs you filed under the project keep their results and keep their project tag; the project itself, its other members and its creator are unaffected.