Staging login still has old redirect

[eyeseast]

It's going to https://www.staging.documentcloud.org/app, which doesn't exist anymore.

[mitchelljkotler]

Do we want it to go to https://muckcloud.com/app? Or do we want it to go to the deploy preview you came from? Which cannot be done statically and would need to be passed in some how.

[eyeseast]

Ideally it goes to the deploy preview (root URL, since /app is gone). We can figure out how to pass that in on the frontend if the backend picks it up.