implement copy building settings with shift + click gesture

src/ui/GameWorldView.h

@@ -14,6 +14,7 @@
 #include <QVector2D>
 
 #include "Blueprint.h"
+#include "BuildingConfig.h"
 #include "BlueprintModeExitedEvent.h"
 #include "BlueprintPlacementRequestedEvent.h"
 #include "BuilderModeExitedEvent.h"
@@ -165,6 +166,12 @@ private:
     void                     stepSpeed(int delta);
     void                     placeAtTile(QPoint tile);
 
+    // Copy-settings gesture (REQ-BLD-COPY-CONFIG): Shift+right-click copies a
+    // building's configuration into m_copiedConfig; Shift+left-click applies it to
+    // another building of the same type via the existing configuration commands.
+    void     copyConfigFrom(BuildingId id);
+    void     pasteConfigTo(BuildingId id);
+
     void     enterBuilderMode(BuildingType type);
     void     exitBuilderMode();
     void     enterBlueprintMode(Blueprint blueprint);
@@ -215,6 +222,10 @@ private:
     std::optional<Blueprint> m_blueprintMode;
     QPoint                   m_blueprintGhostTile;
 
+    // Temporary cache for the copy-settings gesture (REQ-BLD-COPY-CONFIG); held
+    // only while Shift is down and cleared on Shift release.
+    std::optional<BuildingConfig> m_copiedConfig;
+
     bool     m_demolishMode;
     BuildingId m_demolishHoverBuildingId;
     bool     m_debugDraw;