refactor(sandbox): renamed files to stories

packages/pinball_components/sandbox/lib/main.dart

@@ -6,7 +6,6 @@
 // https://opensource.org/licenses/MIT.
 import 'package:dashbook/dashbook.dart';
 import 'package:flutter/material.dart';
-import 'package:sandbox/stories/spaceship/spaceship.dart';
 import 'package:sandbox/stories/stories.dart';
 
 void main() {

packages/pinball_components/sandbox/lib/stories/stories.dart

@@ -1,7 +1,8 @@
-export 'ball/ball.dart';
-export 'baseboard/baseboard.dart';
+export 'ball/stories.dart';
+export 'baseboard/stories.dart';
 export 'chrome_dino/stories.dart';
-export 'dash_nest_bumper/dash_nest_bumper.dart';
-export 'effects/effects.dart';
-export 'flipper/flipper.dart';
-export 'layer/layer.dart';
+export 'dash_nest_bumper/stories.dart';
+export 'effects/stories.dart';
+export 'flipper/stories.dart';
+export 'layer/stories.dart';
+export 'spaceship/stories.dart';