A failed CivitAI lookup used to drop the entry that the fetch had just
refreshed: the on-demand hash was already computed and stored, but the
client only applied the response entry on success, so the card kept the
stale empty sha256 until a page reload.
- Return the refreshed entry in the error payload when the lookup fails.
- Apply the entry on both outcomes in refreshSingleModelMetadata; the
error toast is unchanged.
- Cover the failed-response path on the handler and the API client.
