feat: enable dev debug toolbar on admin, merchant, and storefront panels

The toolbar was only included in the store base template. Add it to all
frontends so developers can use Ctrl+Alt+D everywhere in dev.

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

app/templates/storefront/base.html

@@ -50,6 +50,9 @@
     {# Base Shop Styles #}
     <link rel="stylesheet" href="{{ url_for('static', path='storefront/css/storefront.css') }}">
 
+    {# Dev debug toolbar (dev only — auto-hides in production, must load early for interceptors) #}
+    <script src="{{ url_for('static', path='shared/js/dev-toolbar.js') }}"></script>
+
     {% block extra_head %}{% endblock %}
 </head>