frontend: App: Add AppContainer story

This change adds a Storybook story for the AppContainer component.

Author: skoeva

frontend/src/components/App/AppContainer.stories.tsx

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2025 The Kubernetes Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { Meta, StoryFn } from '@storybook/react';
+import { http, HttpResponse } from 'msw';
+import React from 'react';
+import { I18nextProvider } from 'react-i18next';
+import { Provider } from 'react-redux';
+import i18n from '../../i18n/config';
+import store from '../../redux/stores/store';
+import AppContainer from './AppContainer';
+
+const withEnv = (Story: React.ComponentType) => {
+  const prev = (window as any).desktopApi;
+  (window as any).desktopApi = {
+    send: () => {},
+    receive: () => {},
+  };
+
+  React.useEffect(() => {
+    return () => {
+      if (prev === undefined) {
+        delete (window as any).desktopApi;
+      } else {
+        (window as any).desktopApi = prev;
+      }
+    };
+  }, []);
+
+  return (
+    <Provider store={store}>
+      <I18nextProvider i18n={i18n}>
+        <Story />
+      </I18nextProvider>
+    </Provider>
+  );
+};
+
+export default {
+  title: 'App/AppContainer',
+  component: AppContainer,
+  decorators: [withEnv],
+  parameters: {
+    layout: 'fullscreen',
+    storyshots: { disable: true },
+    docs: {
+      description: {
+        component:
+          'The root container for the Headlamp application. It sets up routing, global providers, and the main layout. This story primarily verifies that it renders its children correctly.',
+      },
+    },
+    msw: {
+      handlers: [
+        http.get('*/plugins', () => HttpResponse.json([])),
+        http.get('*/config', () => HttpResponse.json({})),
+      ],
+    },
+  },
+} as Meta<typeof AppContainer>;
+
+const Template: StoryFn = args => <AppContainer {...args} />;
+
+export const Default = Template.bind({});