Save additional user preferences

Now that we have the ability to save user preferences (see #689), we can start saving more of them. This issue is to keep track of places where we want to save additional user preferences.

Top-level/sitewide preferences:

- Whether the top panel on the homepage is shown or not
- Whether the list of archived projects is shown or not
- See https://github.com/getodk/central/issues/690#issuecomment-2456743664

Project preferences:

- (?) The sort order of the form list
- It's not clear we want this. We've talked about giving project managers the ability to customize the order of forms in the form list.
- (?) Whether managed or legacy QR codes are shown for app users
- Are we planning to offer legacy QR codes indefinitely? Or will that go away once we add the ability to configure QR codes?