make repair ships standby with rest of fleet if there is no one to repair (instead of advancing towards the enemy stations)

src/lib/ecs/component/StandbyBehavior.h

@@ -0,0 +1,11 @@
+#pragma once
+
+// Fallback for ships with a repair capability: instead of charging the enemy
+// like AdvanceBehavior, the ship holds with its fleet so damaged allies stay in
+// sensor range and it can heal them. Scored just above Advance and below Rally,
+// so it only wins when no more urgent behavior applies. The executor decides the
+// destination (StandbyExecutor).
+struct StandbyBehavior
+{
+    float score = 0.0f;
+};