[NcAppSettingsDialog] [NcAppNavigationItem] Redesign follow-ups

[kra-mo]

Some issues I noticed with #8477 and #8448 that should be fixed before the final release.

Navigation

The selected item is lighter, but the hovered one is darker (the other way around in dark mode). The selected item should also be darker, the same as in the settings dialog and like in the mockup.

Settings Dialog

1. The close button is clipping with the content without a background. It should have one.

2. :hover effects and the pill indicating selection on the sidebar don't animate.
3. The pill is taller than in the regular navigation sidebar and (thus) clips into the border radii. It should look the same as for the regular navigation.

@nfebe

[kra-mo]

I'm not sure where the misunderstanding about the selection color came from. Was it this? #8448 (comment)

The active color should be darker and not opaque in any case.