Update react-day-picker to v9

[skagedal]

Currently, I have to use npm install --force to install packages, because react-day-picker is not marked as compatible with React 19. Upgrading the Day Picker to version 9 fixes this, but introduces a layout problem instead. There are PR:s for an updated version, like this one – I think it's not getting merged because it's also mixing in some other new functionality. I think this is a cleaner example as it focuses on just fixing the styles.