split the selection panel into one card per kind of selection

src/ui/selection/FieldMultiContent.h

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <vector>
+
+#include "entt/entity/entity.hpp"
+
+#include "SelectionContent.h"
+#include "SelectionContentFactory.h"
+
+class QLabel;
+
+// The count summary for a field selection holding more than one object that does not
+// aggregate (REQ-UI-FIELD-MULTI-SELECTION): several actors, or actors together with
+// debris. A count per type, and the debris' summed scrap when debris is part of it.
+class FieldMultiContent : public SelectionContent
+{
+    Q_OBJECT
+
+public:
+    FieldMultiContent(const SelectionContext& context, const SelectionRequest& request,
+                      QWidget* parent = nullptr);
+
+protected:
+    void refreshRuntime() override;
+
+private:
+    std::vector<entt::entity> m_actors;
+    std::vector<entt::entity> m_debris;
+    QLabel*                   m_summaryLabel;
+};