chore(prototype): flip follower/leader positions via MovePath exchange on GUI thread

Rebuild switched off for this run. Callbacks log success per exchange.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

mod/content/overtake_probe.gs.lua

@@ -4,5 +4,8 @@ function data()
 		updateScript = {
 			fileName = "overtake_probe.script@update",
 		},
+		guiUpdateScript = {
+			fileName = "overtake_probe.script@guiUpdate",
+		},
 	}
 end