[ui] Viewer3D: Fix wrong camera up vector initialization

Default camera up should be accurate and consistent with camera view center.
Default camera up vector is not refresh or checked when default camera view center is set.

meshroom/ui/qml/Viewer3D/Viewer3D.qml

@@ -22,7 +22,7 @@ FocusScope {
     readonly property alias mainCamera: mainCamera
 
     readonly property vector3d defaultCamPosition: Qt.vector3d(12.0, 10.0, -12.0)
-    readonly property vector3d defaultCamUpVector: Qt.vector3d(0.0, 1.0, 0.0)
+    readonly property vector3d defaultCamUpVector: Qt.vector3d(-0.358979, 0.861550, 0.358979) // should be accurate, consistent with camera view center
     readonly property vector3d defaultCamViewCenter: Qt.vector3d(0.0, 0.0, 0.0)
 
     readonly property var viewpoint: _reconstruction ? _reconstruction.selectedViewpoint : null