Fix breadcrumb JSON-LD: use absolute URLs for item field

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

templates/base.html.twig

@@ -57,7 +57,7 @@
                 "@type": "ListItem",
                 "position": {{ loop.index }},
                 "name": "{{ breadcrumb.name }}"{% if breadcrumb.url is defined and breadcrumb.url is not empty %},
-                "item": "{{ breadcrumb.url }}"{% endif %}
+                "item": "{{ absolute_url(breadcrumb.url) }}"{% endif %}
             }{% if not loop.last %},{% endif %}
             {% endfor %}
         ]