Improve the Review forgotten cards dialog

## The Review forgotten cards dialog


- [ ] Add a title "Review forgotten cards".
- [ ] Remove "x days" from the description.
- [ ] Add a unit "day"/"days" to the box.
- I decided against input steppers since this input isn't a saved setting. It also allows to add the unit more organically.
- [ ] Replace "OK" with "Create".
- [ ] If the resulting filtered deck is empty (i.e., no cards match the criteria), a red warning should appear and the button should be disabled, instead of an error dialog (see reference).
- [ ] Show a warning when the input is invalid, limit the digits, and prevent leading zeros, like in https://github.com/ankidroid/Anki-Android/pull/20520, except without input steppers.

## Reference dialogs