The package shipped no overrides and only inherited the system
default theme, so it had no visible effect. Authoring a correct
FrameSvg override needs a separate, designed effort.
Add a wallpapers/SHIFT package with light and dark images. Set
Image=SHIFT in the look-and-feel defaults.
Plasma's org.kde.image backend requires a directory URL, not a
bare package ID, when writing Image= in a layout.js. Use
configure_file to stamp the resolved KDE_INSTALL_WALLPAPERDIR
path into the installed layout.js at build time.
