Remove short flicker during the transition from child/command TUI to watchbind's TUI

[fritzrehde]

Once a child/command TUI (spawned with exec tui -- <CMD>) terminates, watchbind temporarily (only for a split-second) returns to the user's terminal and only then paints the screen with watchbind's TUI again. I have found this to be very common, if not always present, in other TUI applications (e.g. file managers like yazi or lf), so maybe this is just a standard issue that can't really be fixed. I also don't think it's a big problem, the transition is so short it's barely noticable. Nevertheless, I will keep an issue here in case someone comes up with a fix someday.