split the selection panel into one card per kind of selection

src/ui/selection/DebrisContent.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <vector>
+
+#include "entt/entity/entity.hpp"
+
+#include "SelectionContent.h"
+#include "SelectionContentFactory.h"
+
+class QLabel;
+
+// The card for selected debris (REQ-UI-DEBRIS-PANEL): the scrap still left in it.
+//
+// It is the field category's aggregating content (REQ-UI-SELECTION-AGGREGATE): several
+// pieces of debris show this same card with the count in the header and their scrap
+// summed, because that is the one value the card holds and it adds up.
+class DebrisContent : public SelectionContent
+{
+    Q_OBJECT
+
+public:
+    DebrisContent(const SelectionContext& context, const SelectionRequest& request,
+                  QWidget* parent = nullptr);
+
+protected:
+    void refreshRuntime() override;
+
+private:
+    std::vector<entt::entity> m_debris;
+    QLabel*                   m_scrapLabel;
+};