perf: add defer to scripts and lazy loading to images

Add defer attribute to 145 <script> tags across 103 template files
(PERF-067) and loading="lazy" to 22 <img> tags across 13 template
files (PERF-058). Both improve page load performance.

Validator totals: 0 errors, 2 warnings, 1360 info (down from 1527).

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

app/modules/orders/templates/orders/admin/orders.html

@@ -641,5 +641,5 @@
 {% endblock %}
 
 {% block extra_scripts %}
-<script src="{{ url_for('orders_static', path='admin/js/orders.js') }}"></script>
+<script defer src="{{ url_for('orders_static', path='admin/js/orders.js') }}"></script>
 {% endblock %}

app/modules/orders/templates/orders/store/invoices.html

@@ -10,7 +10,7 @@
 {% block alpine_data %}storeInvoices(){% endblock %}
 
 {% block extra_scripts %}
-<script src="/static/modules/billing/store/js/invoices.js"></script>
+<script defer src="/static/modules/billing/store/js/invoices.js"></script>
 {% endblock %}
 
 {% block content %}

app/modules/orders/templates/orders/store/order-detail.html

@@ -451,5 +451,5 @@
         orderId: {{ order_id }}
     };
 </script>
-<script src="{{ url_for('orders_static', path='store/js/order-detail.js') }}"></script>
+<script defer src="{{ url_for('orders_static', path='store/js/order-detail.js') }}"></script>
 {% endblock %}

app/modules/orders/templates/orders/store/orders.html

@@ -330,5 +330,5 @@
 {% endblock %}
 
 {% block extra_scripts %}
-<script src="{{ url_for('orders_static', path='store/js/orders.js') }}"></script>
+<script defer src="{{ url_for('orders_static', path='store/js/orders.js') }}"></script>
 {% endblock %}