fix(issues): Preserve loaded events after refresh failures (#126109)

Keep an already loaded event visible when a background refresh fails
with a retryable error. #125343 treated React Query's refetch error as
an initial-load failure, replacing cached event details with the error
screen.

Requests without cached event data still show the recoverable error, and
validation or permission errors still block the event view. Regression
coverage checks cached event data after a 503 or 403 refresh failure.