viewer: keep plot axis labels readable when compressed

When the plot dock was short, Qt Charts dropped the axis labels first, making
the plot hard to read.

- Reclaim Qt Charts' outer graphics-layout padding and trim the inner margins
  (both chart views) so the plot and its labels get the available space.
- Raise the chart minimum height (dataset-info 80 -> 140, per-image 120 -> 140)
  so the dock can't be squeezed below the point where the axis labels fit.

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

viewer/charts/JFJochDatasetInfoChartView.cpp

@@ -6,12 +6,18 @@
 #include <QClipboard>
 #include <QCategoryAxis>
 #include <QtCharts/QLegendMarker>
+#include <QGraphicsLayout>
 
 #include "JFJochDatasetInfoChartView.h"
 
 JFJochDatasetInfoChartView::JFJochDatasetInfoChartView(QWidget *parent)
     : QChartView(new QChart(), parent) {
     chart()->legend()->hide();
+    // Reclaim Qt Charts' outer layout padding and trim the inner margins so the axis labels keep
+    // their room even when the dock is short (otherwise they are the first thing Qt drops).
+    chart()->layout()->setContentsMargins(0, 0, 0, 0);
+    chart()->setMargins(QMargins(2, 2, 6, 2));
+    chart()->setBackgroundRoundness(0);
     setRenderHint(QPainter::Antialiasing);
    // setRubberBand(QChartView::RubberBand::RectangleRubberBand);
     setMouseTracking(true);