Move CountDownTimer logic from a Dialog into a ForegroundService so
the timer survives when the user tabs away or the activity is
destroyed. The activity becomes a thin UI projection bound to the
service via TimerStateListener callbacks.
- Create CountdownService with notification, state persistence,
and ToneGenerator/Vibrator ownership
- Persist timer state to SharedPreferences for process death recovery
- Add notification with progress bar and Stop/Restart actions
- Embed countdown UI in activity_main.xml alongside picker UI
- Delete CountdownDialog and dialog_countdown.xml
- Update AndroidManifest with foreground service permissions
kfj001