allow to set the recipe already for construction sites

src/ui/SelectedBuildingPanel.h

@@ -9,6 +9,7 @@
 
 #include "entt/entity/entity.hpp"
 
+#include "BeltSystem.h"
 #include "Building.h"
 #include "BuildingId.h"
 #include "DebugDrawToggledEvent.h"
@@ -63,7 +64,7 @@ private:
     void buildSingle(BuildingId id);
     void buildMulti(const std::vector<BuildingId>& ids);
     void refreshBuffers(const Building* b);
-    void buildSplitterFilters(QPoint splitterTile);
+    void buildSplitterFilters(const std::optional<BeltSystem::SplitterInfo>& info);
     const RecipeDef* findRecipe(const Building* b) const;
     const ShipDef*   findShipDef(const std::string& id) const;
     std::vector<std::string> allItemIds() const;
@@ -86,6 +87,7 @@ private:
     QPushButton*       m_configureLayoutBtn;
 
     BuildingId     m_singleBuildingId;
+    bool         m_singleIsSite = false;  // selected single entity is a construction site
     QPoint       m_splitterTile;
     std::string  m_currentRecipeId;