Make a great first-user experience

[ErikBjare]

To avoid situations like this for aw-qt, where people expect a window to open and don't notice the tray icon: https://forum.activitywatch.net/t/activity-watch-wont-launch-on-windows/1389

Possible features, in increasing order of difficulty:

• When app is started and already running, open webview.
• Add notification when ActivityWatch starts (as we used to), add setting to turn it off.
• Proper onboarding experience when app is started for the first time (or onboarding never shown), introducing ActivityWatch and the tray icon.

[brayo-pip]

Isn't the first one already implemented by default? Currently when you launch the aw-tauri the webview opens and then when you close it minimizes to trayicon.