Report Svelte errors

[matthew-ia]

Think I'm forgetting to surface Svelte errors—just get "could not prerender page" when I'm pretty sure Svelte would say something more specific.

[matthew-ia]

Also consider that when there's a compilation error in Rollup for a Cayo component, these don't get surfaced for some reason—only if you're prerendering the component (not a Cayo) does it show the Rollup message.