switch to ECS architecture

src/lib/sim/Building.h

@@ -10,6 +10,8 @@
 
 #include "BuildingType.h"
 #include "EntityId.h"
+
+#include "entt/entity/entity.hpp"
 #include "Item.h"
 #include "ItemType.h"
 #include "Port.h"
@@ -62,7 +64,7 @@ struct StationWeapon
     float range;
     float fireRateHz;
     float cooldownTicks;
-    std::optional<EntityId> currentTarget;
+    std::optional<entt::entity> currentTarget;
 };
 
 // A fully constructed, operational building.