openSUSE Tumbleweed's plasma6-nm 6.6.4 does not ship the org.kde.plasma.networkmanagement.cellular QML submodule that SignalStrengthInfo.qml imports unconditionally. Without it the MobileShell QML namespace fails to load and preview boots to a black screen.
Keep a minimal fallback module under tools/preview-stubs and install it only for local .prefix preview installs by default, with SHIFT_INSTALL_PREVIEW_QML_STUBS=AUTO/ON/OFF for explicit control. Add a CTest guard so qmldir entries stay backed by real files and the fallback remains tied to the QML import tree.
