fetch-data: Update old fetch data automatically.

Set up a time-based refresh rate of fetch data to keep it current.
Also, perhaps employ the window focus/blur events to avoid polling while the browser isn't in focus.

Start by locating the fetch-data implementation and the browser lifecycle handling it uses. Determine the required refresh interval and how focus/blur should affect polling; done means stale fetch data refreshes automatically while background polling is avoided when the browser is unfocused.

Written by the indexing model from the issue text.