fix: wrap UI updates in fyne.Do for thread safety

Since Fyne 2.6, UI modifications from background goroutines must be
wrapped in fyne.Do() to run on the main thread. The OnTick and OnEnd
callbacks are called from the pomodoro ticker goroutine, causing thread
safety warnings.

Author: tomsquest

ui/ui.go

@@ -127,13 +127,17 @@ func MakeClassicLayout(thePomodoro *pomodoro.Pomodoro) fyne.CanvasObject {
 	}
 
 	thePomodoro.OnTick = func() {
-		setTimerRemainingTime(thePomodoro, timer)
+		fyne.Do(func() {
+			setTimerRemainingTime(thePomodoro, timer)
+		})
 	}
 	thePomodoro.OnEnd = func(kind pomodoro.Kind) {
-		setTimerRemainingTime(thePomodoro, timer)
+		fyne.Do(func() {
+			setTimerRemainingTime(thePomodoro, timer)
 
-		playButton.Icon = theme.MediaPlayIcon()
-		playButton.Refresh()
+			playButton.Icon = theme.MediaPlayIcon()
+			playButton.Refresh()
+		})
 
 		notifyPomodoroDone(kind)
 	}