[kde-kit] Our KDE's `kde-plasma/oxygen` does not have the notification sounds

The notifications are defined, but they don't play. Investigation reveals that the sound files which are supposed to be in `/usr/share/sounds/` don't exist. Example: `/usr/share/sounds/Oxygen-Sys-App-Positive.ogg`. Plasma-6 has a package `oxygen-sounds` that probably contains what we want, so that's a good place to look, if they're not already present in the `oxygen` package's not-installed files.

Start by inspecting the kde-kit/oxygen package contents and comparing them with the Plasma-6 oxygen-sounds package. Verify whether files such as /usr/share/sounds/Oxygen-Sys-App-Positive.ogg are provided, and consider the issue complete when the notification sound files are installed and available at the expected paths.

Written by the indexing model from the issue text.