Fix useSyncLocalStorage initial value loss

[tmns]

Currently useSyncLocalStorage does not actually set the initial value in local storage, even though the comment here implies it does.

Relatedly, since the item never actually exists in storage, if the user updates some other item, and the effect here runs, the hook will start returning null for the value instead of the initial value. This can also of course happen if the user clears their storage / deletes said item, and subsequently updates another item.

I think expected behavior would be a) for the initial value to actually get saved in storage, and b) for the hook to revert back to returning the initial value when the item's been deleted. Open to other approaches though!

Realized this while working on some orderbook changes. When using this hook to manage the display preference (i.e. vertical / horizontal), the app will break if the user hasn't explicitly updated this preference and performs some action to trigger a storage update (e.g. change order type).