move ecs related code to own folder

src/lib/ecs/system/AiSystem.h

@@ -0,0 +1,14 @@
+#pragma once
+
+class BuildingSystem;
+class EntityAdmin;
+class ScrapSystem;
+
+class AiSystem
+{
+public:
+    void tickHomeReturnBehavior(EntityAdmin& admin);
+    void tickThreatResponseBehavior(EntityAdmin& admin, const BuildingSystem& buildings);
+    void tickRepairBehavior(EntityAdmin& admin, BuildingSystem& buildings);
+    void tickSalvageBehavior(EntityAdmin& admin, ScrapSystem& scraps, BuildingSystem& buildings);
+};