applets/notifications: Tint header for critical notifications
Requires https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/348.
We get intermittent user complaints and bug reports about notifications not being visible enough, especially on large or cluttered screens.
This commit attempts to remedy the situation by tinting the header for critical notifications to use the color-scheme-specified "warning" color. Only critical notifications receive this treatment since they're the only ones that the user really does need to see.
BUG: 420541 FIXED-IN: 5.24
cc @teams/vdg
Edited by Nate Graham