feat(storybook): add a global decorator for stories

.storybook/preview.ts

@@ -1,9 +1,10 @@
 import type { Preview } from '@storybook/svelte-vite';
-
+import StoryStage from './StoryStage.svelte';
 import '../src/app/styles/app.css';
 
 const preview: Preview = {
     parameters: {
+        layout: 'fullscreen',
         controls: {
             matchers: {
                 color: /(background|color)$/i,
@@ -18,6 +19,21 @@ const preview: Preview = {
             test: 'todo',
         },
     },
+    decorators: [
+        (storyFn, { parameters }) => {
+            const { Component, props } = storyFn();
+            return {
+                Component: StoryStage,
+                // We pass the actual story component into the Stage via a snippet/slot
+                // Svelte 5 Storybook handles this mapping internally when you return this structure
+                props: {
+                    children: Component,
+                    width: parameters.stageWidth || 'max-w-3xl',
+                    ...props,
+                },
+            };
+        },
+    ],
 };
 
 export default preview;