allow multi-select for ships/stations, mixable with scrap

src/balancing/ArenaView.cpp

@@ -15,7 +15,7 @@
 #include "Building.h"
 #include "BuildingSystem.h"
 #include "EntityHitTest.h"
-#include "EntitySelectedEvent.h"
+#include "EntitySelectionChangedEvent.h"
 #include "EventManager.h"
 #include "FacingComponent.h"
 #include "FactionComponent.h"
@@ -259,8 +259,14 @@ void ArenaView::mousePressEvent(QMouseEvent* event)
             m_selectedEntity = std::nullopt;
         }
 
+        // The arena is strictly single-select; emit a vector of size 0 or 1.
+        std::vector<entt::entity> selection;
+        if (m_selectedEntity.has_value())
+        {
+            selection.push_back(*m_selectedEntity);
+        }
         EventManager::getInstance()->sendEventImmediately(
-            std::make_shared<EntitySelectedEvent>(m_selectedEntity));
+            std::make_shared<EntitySelectionChangedEvent>(selection));
     }
 
     QOpenGLWidget::mousePressEvent(event);