fix(storefront): add icons.js to storefront login page

The storefront login template uses $icon() in Alpine expressions but
didn't load icons.js, causing "$icon is not defined" errors.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/customers/templates/customers/storefront/login.html

@@ -181,6 +181,9 @@
         </div>
     </div>
 
+    <!-- Icons (registers $icon magic helper for Alpine) -->
+    <script defer src="{{ url_for('static', path='shared/js/icons.js') }}"></script>
+
     <!-- Alpine.js v3 -->
     <script defer src="https://cdn.jsdelivr.net/npm/alpinejs@3.14.0/dist/cdn.min.js"></script>