refactor: rename shopLayoutData to storefrontLayoutData

Align Alpine.js base component naming with storefront terminology.
Updated across all storefront JS, templates, and documentation.

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

app/modules/checkout/templates/checkout/storefront/checkout.html

@@ -477,7 +477,7 @@
 <script>
 function checkoutPage() {
     return {
-        ...shopLayoutData(),
+        ...storefrontLayoutData(),
 
         // State
         loading: true,
@@ -595,8 +595,8 @@ function checkoutPage() {
             console.log('[CHECKOUT] Initializing...');
 
             // Initialize session
-            if (typeof shopLayoutData === 'function') {
-                const baseData = shopLayoutData();
+            if (typeof storefrontLayoutData === 'function') {
+                const baseData = storefrontLayoutData();
                 if (baseData.init) {
                     baseData.init.call(this);
                 }