Add a favicon

Crops the key/globe mark out of the existing logo and wires it into
base.html.twig as favicon.ico plus PNG/apple-touch-icon variants.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

templates/base.html.twig

@@ -4,6 +4,10 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>{% block title %}{{ 'site.name'|trans }}{% endblock %}</title>
+    <link rel="icon" href="{{ asset('favicon.ico') }}" sizes="any">
+    <link rel="icon" type="image/png" sizes="32x32" href="{{ asset('images/favicon-32x32.png') }}">
+    <link rel="icon" type="image/png" sizes="16x16" href="{{ asset('images/favicon-16x16.png') }}">
+    <link rel="apple-touch-icon" href="{{ asset('images/apple-touch-icon.png') }}">
     {% block stylesheets %}
         {{ encore_entry_link_tags('app') }}
     {% endblock %}