viewer: add/subtract the selected ROI to/from the user mask

Restore the ROI-to-mask action on the new list: "Add to mask" and
"Subtract from mask" buttons rasterise the selected ROI into the user
mask (set or clear), through the same UpdateUserMask_i path. The ROI is
evaluated with per-pixel resolution and phi from the geometry, so box,
circle and azimuthal (sector) ROIs all map correctly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

viewer/JFJochViewerSidePanel.cpp

@@ -132,6 +132,7 @@ JFJochViewerSidePanel::JFJochViewerSidePanel(QWidget *parent) : QWidget(parent)
     connect(roi_list, &JFJochViewerROIList::selectedROIChanged, this, &JFJochViewerSidePanel::selectedROIChanged);
     connect(roi_list, &JFJochViewerROIList::downloadROIs, this, &JFJochViewerSidePanel::downloadROIs);
     connect(roi_list, &JFJochViewerROIList::uploadROIs, this, &JFJochViewerSidePanel::uploadROIs);
+    connect(roi_list, &JFJochViewerROIList::maskFromROI, this, &JFJochViewerSidePanel::maskFromROI);
 
     layout->addWidget(new TitleLabel("Data analysis", this));