refactor AI system

src/lib/ecs/system/ai/RetreatEvaluator.h

@@ -0,0 +1,12 @@
+#pragma once
+
+class EntityAdmin;
+
+// Scores high (above all task behaviors) when the ship's health is below its
+// retreat threshold, or when an enemy ship is within sensor range and the ship
+// has no weapons to fight back with.
+class RetreatEvaluator
+{
+public:
+    void evaluate(EntityAdmin& admin);
+};