Loader spinner should better handle when the user quits the server

[bitspittle]

1. kobweb run
2. change some code
3. while "building..." spinner is up, press Q

Expected: Page indicates that the web server is down Actual: Spinner keeps going forever

[bitspittle]

This might have been exacerbated by an internal compiler error with compose, which apparently caused Gradle's -t option to stop working, so when I pressed "Q" to exit the server, everything was already busted. This may be a rare thing for users to run into themselves, so it may not be an urgent issue.

[bitspittle]

Maybe the easier bug here is that if the client sees that the server is down (at least in dev mode), it should kill the current page and render something like "The server cannot be reached"