better error when using read with adapter-auto

[Rich-Harris]

Describe the problem

If someone uses the new read function in a default project, it will fail immediately with the following error:

Cannot use read from $app/server in when using @sveltejs/adapter-auto. Please ensure that your adapter is up to date and supports this feature.

This could be more helpful

Describe the proposed solution

Add a supports.read function to adapter-auto that throws a more helpful error. Something like

The read function imported from $app/server only works in certain environments. Since you're using @sveltejs/adapter-auto, SvelteKit cannot determine whether it will work when your app is deployed. Please replace it with an adapter tailored to your target environment.