Improve the Preview new cards dialog

- [ ] Add a title "Preview new cards".
- [ ] Replace the description with "Preview new cards added in the last:".
- [ ] Add a unit "day"/"days" to the box.
- [ ] 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.