Feature request: `Quit` option for system tray

It would be nice if there was a "Quit" option on the system tray icon to easily close the application, so the current process that requires 4 clicks to quit could be avoided.

While not required, one possible additional part of this button would be a confirmation dialog to ensure that the user did not accidentally click the "Quit" button.

Ref: https://github.com/keybase/client/issues/3773#issuecomment-863308150

The issue names no files, tests, or entry points. Start by locating the system tray implementation for the desktop application and trace the existing four-click quit flow. Done means the tray icon exposes a Quit action and any confirmation behavior is defined and tested.

Written by the indexing model from the issue text.