Save The Tree implementation and acceptance work in progress

Preserve production code, regression fixtures, audio assets and provenance, test infrastructure, and the original-completion plan and progress ledger. Final game and Windows acceptance remain pending; excluded local artifacts and native experiments are not part of this snapshot.

tests/ui/test_main_dashboard.gd

@@ -1,5 +1,7 @@
 extends SceneTree
 
+const AudioTeardown := preload("res://tests/helpers/ui_audio_teardown.gd")
+
 var _manual_save_path := "user://tests/main_dashboard_%d/manual_ui" % OS.get_process_id()
 var _checks := 0
 var _failures := 0
@@ -202,8 +204,8 @@ func _run() -> void:
 	_test_manual_save_and_load()
 	_test_event_choice_ui()
 
-	if is_instance_valid(_main):
-		_main.queue_free()
+	var teardown: Dictionary = await AudioTeardown.free_owner_and_wait(self, _main)
+	_expect(bool(teardown.get(&"passed", false)) and not bool(teardown.get(&"deadline_reached", true)), "owned audio references release before bounded teardown deadline with whole Runtime unchanged")
 	SaveService.delete_save(_manual_save_path)
 	if _failures == 0:
 		print("PASS: %d checks" % _checks)