Initial commit: Grav CMS setup with HTML reference material

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

user/plugins/admin/themes/grav/templates/error.html.twig

@@ -0,0 +1,20 @@
+{% extends 'partials/base.html.twig' %}
+
+{% block titlebar %}
+    <h1><i class="fa fa-fw fa-exclamation-triangle"></i> {{ "PLUGIN_ADMIN.ERROR"|t }}</h1>
+{% endblock %}
+
+{% block content %}
+<div class="error-block">
+    <h1>Error {{ page.header.http_response_code }}</h1>
+    <div class="padding">
+    <p>
+        {{ page.content|raw }}
+    </p>
+    </div>
+</div>
+{% endblock %}
+
+{% block footer_section %}
+<br /><br /><br />
+{% endblock %}