fix(public-docsite-v9-headless): fix root import in tailwind sandbox template

The sandbox App template was importing Provider from the package root which
caused Vite to fail with "Missing '.' specifier" since the package only
exposes sub-path exports. Fixed to use the correct sub-path import.

Reproduction: https://stackblitz.com/edit/eu9cefke?file=src%2Fexample.tsx

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dmytrokirpa

apps/public-docsite-v9-headless/.storybook/preview.js

@@ -24,6 +24,19 @@ export const parameters = {
     ...rootPreview.parameters.exportToSandbox,
     ...tailwindSandboxTemplate,
   },
+  reactStorybookAddon: {
+    docs: {
+      argTable: {
+        slotsApi: true,
+        nativePropsApi: true,
+      },
+      copyAsMarkdown: true,
+      tableOfContents: true,
+      dirSwitcher: true,
+      // headless components don't support theming
+      themePicker: false,
+    },
+  },
 };
 
 export const tags = ['autodocs'];

apps/public-docsite-v9-headless/.storybook/tailwind-sandbox-template.js

@@ -1,4 +1,4 @@
-const sandboxApp = `import { Provider } from '@fluentui/react-headless-components-preview';
+const sandboxApp = `import { Provider } from '@fluentui/react-headless-components-preview/provider';
 import { Example } from './example';
 
 const App = () => (