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_staff_rest.gd

@@ -1,4 +1,5 @@
 extends SceneTree
+const FixtureCleanup := preload("res://tests/helpers/ui_audio_fixture_cleanup.gd")
 var checks := 0
 var failures := 0
 func _initialize() -> void: call_deferred("run")
@@ -35,5 +36,10 @@ func run() -> void:
 		main.world_preview.queue_redraw();await process_frame;await RenderingServer.frame_post_draw
 		expect(root.get_texture().get_image().save_png("res://artifacts/remaining-2026-09-29/staff-rest.png") == OK,"resting staff screenshot saved")
 	expect(runtime.restore_snapshot(runtime.create_snapshot()),"visible rest state remains saveable")
-	main.queue_free();await process_frame
+	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
+	await process_frame
 	print("Staff rest UI: %d checks, %d failures" % [checks,failures]);quit(failures)