feat(analytics): add OpenPanel tracking to storefront

Add comprehensive OpenPanel analytics tracking:
- Install @openpanel/nextjs SDK
- Add OpenPanelComponent to root layout for automatic page views
- Create useAnalytics hook for tracking custom events
- Track checkout funnel: started, shipping step, order completed
- Track product views and add-to-cart events
- Identify users on order completion
- Add NEXT_PUBLIC_OPENPANEL_CLIENT_ID to environment

package.json

@@ -10,6 +10,7 @@
   },
   "dependencies": {
     "@apollo/client": "^4.1.6",
+    "@openpanel/nextjs": "^1.4.0",
     "@react-email/components": "^1.0.10",
     "@react-email/render": "^2.0.4",
     "clsx": "^2.1.1",