Retry sync on network error

We should add automatic retries (with backoff) of sync requests so that an intermittent network issue doesn't cause a sync of a large number of items to fail.

Example from #710:

<img width="296" height="143" alt="Image" src="https://github.com/user-attachments/assets/a0b6ac77-c5cc-4839-acb7-a43ef1b687f8" />
