viewer: Phase 1c — fold per-image plot into the dataset-info dock

Remove the duplicated per-image plot from the side panel and host it in the
dataset-info dock instead:

- JFJochViewerDatasetInfo gains a "Per-image" toggle (next to Grid) that swaps
  the stacked view to the existing JFJochViewerSidePanelChart (azimuthal 1D,
  Wilson, I/sigma, spot and fluorescence profiles of the current image). The
  per-dataset metric combo is disabled while in per-image mode.
- The per-image profile follows the displayed image (imageLoaded forwarded).
- Drop the "Image statistics plot" section from JFJochViewerSidePanel.

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

viewer/JFJochViewerSidePanel.cpp

@@ -99,16 +99,8 @@ JFJochViewerSidePanel::JFJochViewerSidePanel(QWidget *parent) : QWidget(parent)
 
     layout->addWidget(res_rings);
 
-    layout->addWidget(new TitleLabel("Image statistics plot", this));
-    chart = new JFJochViewerSidePanelChart(this);
-    layout->addWidget(chart);
-
-    connect(this, &JFJochViewerSidePanel::imageLoaded,
-            chart, &JFJochViewerSidePanelChart::loadImage);
-    connect(chart, &JFJochViewerSidePanelChart::writeStatusBar,
-    [&] (QString string, int timeout_ms) {
-        emit writeStatusBar(string, timeout_ms);
-    });
+    // The per-image statistics plot now lives in the dataset-info dock (its "Per-image" toggle),
+    // so it is no longer duplicated here.
 
     layout->addWidget(new TitleLabel("ROI", this));