AI Assistant: Better UI when assistant is unavailable

When I start lightning in dev mode with no apollo server, the AI assistant is disabled - but I get no visual feedback about this. I am simply unable to get a caret inside the text editor - which is actually a little annoying. The assistant feels totally broken.

This is a total disaster if it happens to a user. But in practice I'm not sure how important this one is. I see it in local dev all the time. But users shouldn't ever see it on app.openfn.org. Deployments which have not set up AI will also see it (and that's worth worrying about).

I know there's a desire to show a disabled assistant as a marketing feature, but I think that's really bad UX (and actually I think it's pretty cynical design).

There are two different states, right?

1. The deployment has not configured the AI assistant (so I think we should hide it completely from the UI)
2. The deployment has configured the assistant but the apollo server is not available.

This issue is focused on point 2.

Start by reproducing Lightning in dev mode without an Apollo server and inspect how the AI assistant and text editor behave when the assistant is unavailable. Compare the configured-but-unavailable state with the unconfigured state described in the issue. Done means users receive clear visual feedback instead of an apparently broken editor when the configured assistant cannot connect.