Server-side storage support for todo widget

Already implemented in PR #838, which enhances the todo widget functionality by adding support for server-side storage, allowing todo tasks to be persisted and synced across different devices and browsers.

Start by reviewing PR #838, which the issue says already implements server-side storage for the todo widget. Compare that work with the issue's stated goal of persisting and syncing tasks across devices and browsers; the issue is complete when that functionality is covered by the existing implementation.

Written by the indexing model from the issue text.