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_defense_management.gd

@@ -1,4 +1,5 @@
 extends SceneTree
+const FixtureCleanup := preload("res://tests/helpers/ui_audio_fixture_cleanup.gd")
 
 ## Command-backed UI acceptance. Incidents are disclosed threat fixtures;
 ## combat progression uses the ordinary game clock.
@@ -196,7 +197,12 @@ func _create_incident(id: StringName) -> CommandResult:
 
 
 func _finish() -> void:
-	if is_instance_valid(_main): _main.queue_free()
+	if is_instance_valid(_main):
+		var _audio_cleanup_final: Dictionary = await FixtureCleanup.free_owner_and_wait(self, _main)
+		if not bool(_audio_cleanup_final.get(&"passed", false)):
+			push_error("Ordinary fixture audio cleanup failed: %s" % str(_audio_cleanup_final))
+			quit(96)
+			return
 	for path: String in _slots:
 		SaveService.delete_save(path)
 	if _failures == 0: print("PASS: %d checks" % _checks)