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

src/app/[locale]/checkout/page.tsx

@@ -10,6 +10,7 @@ import Footer from "@/components/layout/Footer";
 import { useSaleorCheckoutStore } from "@/stores/saleorCheckoutStore";
 import { formatPrice } from "@/lib/saleor";
 import { saleorClient } from "@/lib/saleor/client";
+import { useAnalytics } from "@/lib/analytics";
 import {
   CHECKOUT_SHIPPING_ADDRESS_UPDATE,
   CHECKOUT_BILLING_ADDRESS_UPDATE,
@@ -96,6 +97,7 @@ export default function CheckoutPage() {
   const locale = useLocale();
   const router = useRouter();
   const { checkout, refreshCheckout, getLines, getTotal } = useSaleorCheckoutStore();
+  const { trackCheckoutStarted, trackCheckoutStep, trackOrderCompleted, identifyUser } = useAnalytics();
   const [isLoading, setIsLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [orderComplete, setOrderComplete] = useState(false);
@@ -138,6 +140,25 @@ export default function CheckoutPage() {
     }
   }, [checkout, refreshCheckout]);
 
+  // Track checkout started when page loads
+  useEffect(() => {
+    if (checkout) {
+      const lines = getLines();
+      const total = getTotal();
+      trackCheckoutStarted({
+        total,
+        currency: "RSD",
+        item_count: lines.reduce((sum, line) => sum + line.quantity, 0),
+        items: lines.map(line => ({
+          id: line.variant.id,
+          name: line.variant.product.name,
+          quantity: line.quantity,
+          price: line.variant.pricing?.price?.gross?.amount || 0,
+        })),
+      });
+    }
+  }, [checkout]);
+
   // Scroll to top when order is complete
   useEffect(() => {
     if (orderComplete) {
@@ -257,6 +278,27 @@ export default function CheckoutPage() {
         if (order) {
           setOrderNumber(order.number);
           setOrderComplete(true);
+          
+          // Track order completion
+          const lines = getLines();
+          const total = getTotal();
+          trackOrderCompleted({
+            order_id: checkout.id,
+            order_number: order.number,
+            total,
+            currency: "RSD",
+            item_count: lines.reduce((sum, line) => sum + line.quantity, 0),
+            shipping_cost: shippingMethods.find(m => m.id === selectedShippingMethod)?.price.amount,
+            customer_email: shippingAddress.email,
+          });
+          
+          // Identify the user
+          identifyUser({
+            profileId: shippingAddress.email,
+            email: shippingAddress.email,
+            firstName: shippingAddress.firstName,
+            lastName: shippingAddress.lastName,
+          });
         } else {
           throw new Error(t("errorCreatingOrder"));
         }
@@ -330,6 +372,11 @@ export default function CheckoutPage() {
         setShippingMethods(availableMethods);
         setShowShippingMethods(true);
         
+        // Track shipping step
+        trackCheckoutStep("shipping_method_selection", {
+          available_methods_count: availableMethods.length,
+        });
+        
         // Don't complete yet - show shipping method selection
         console.log("Phase 1 complete. Waiting for shipping method selection...");
       }