Keep the dashboard and its last-loaded data visible during temporary
network interruptions instead of replacing it with a full-page error.
Show a disconnected banner with a Refresh button and retry failed loader
reads automatically.

Only same-origin GET loader requests are retried. Mutations, server
errors, and canceled requests retain their existing behavior. Refresh
revalidates page data without reloading the document.

Mono-RevId: e1dfee3bf53edcae410ee0b482ff127345ec802c