Remember focus mode status upon restart

### What

Please consider making the focus mode a configurable setting that is stored (and restored) across app restarts.

### Why

I'd argue that the focus mode is a permanent personal preference that goes beyond wanting to momentarily hide the notes list and then show it again.

I myself find that having to switch to focus mode every time the app is started is not very effective and slightly irritating (my own personal bias, though!).

The default is non-focus mode, but I could imagine that some users could benefit from effectively being able to choose which default works best for them (focus mode or non-focus mode).

### How

Make focus mode a configurable setting that is stored and loaded at the time the app is started.

Thanks for listening!

The issue names no files, tests, or entry points. Start by locating the focus-mode state and the app’s existing persisted-settings and startup-restore paths. Done means users can choose focus or non-focus mode, that choice is stored, and the same mode is restored after restarting the app.

Written by the indexing model from the issue text.