Remember mode across app launches

[marksftw]

We should persist whether the user is in Chat Mode or Agent Mode across launches of the app. This would be especially helpful in development when I'm launching the app dozens of times.

Local storage of the selection is fine, no need to persist on the server.

[marksftw]

I’m working on this now. I’ll implement local persistence for the selected Chat/Agent mode and verify it by rebuilding and relaunching the desktop app across multiple mode changes.