switch to ECS architecture

src/lib/sim/BuildingSystem.h

@@ -96,6 +96,10 @@ public:
     // Find nearest operational building of the given type; nullptr if none.
     const Building* findNearestBuilding(QVector2D worldPos, BuildingType type) const;
 
+    // Register / unregister tile occupancy for ECS station entities.
+    void registerTileOccupancy(const std::vector<QPoint>& cells, EntityId ownerPlaceholder);
+    void unregisterTileOccupancy(const std::vector<QPoint>& cells);
+
     // Place one "scrap" item into a SalvageBay's output buffer.
     // Returns false if bay not found, wrong type, or output buffer is full.
     bool deliverScrapToSalvageBay(EntityId bayId);