refactor(gameplay): separate player logic into manager and ECS components

include/Cubed/gameplay/ecs/entity.hpp

@@ -0,0 +1,11 @@
+#pragma once
+#include <cstdint>
+namespace Cubed {
+using EntityID = uint64_t;
+
+struct Entity {
+    EntityID id;
+    explicit Entity(EntityID id) : id(id) {}
+};
+
+} // namespace Cubed