Make Backend Errors More Obvious in Dev

When running convex in dev mode and making changes that lead to an error (like a type error), its currently very easy to overlook that problem, because the error is only surfaced in the terminal where the dev process is running and the convex deployment just remains in it's previous state. It's pretty common to have the terminal with the dev process somewhere in the background/minimized and not looking at it at all times. Ideally there should be some indicator that the convex deployment is in an error state in the UI or other consumers of the convex deployment. For example an error popup in the UI. And/or potentially making all operations against the convex deployment fail until the next successful build.