Initial commit: Grav CMS setup with HTML reference material

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

plugins/admin/themes/grav/templates/login.html.twig

@@ -0,0 +1,11 @@
+{% set user = grav.user %}
+
+{% if user.username and user.authenticated %}
+    {% if not user.authorized and user.twofa_enabled %}
+        {% include 'partials/login-twofa.html.twig' %}
+    {% else %}
+        {% include 'partials/login-logout.html.twig' %}
+    {% endif %}
+{% else %}
+    {% include 'partials/login-form.html.twig' %}
+{% endif %}