[Web] Add sogo_auth_internal nginx marker for sogo-auth.php

data/conf/nginx/templates/sites-default.conf.j2

@@ -116,6 +116,8 @@ location ~ \.php$ {
     include /etc/nginx/fastcgi_params;
     fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
     fastcgi_param PATH_INFO $fastcgi_path_info;
+    # trusted internal-auth marker; empty for external clients (see nginx.conf map)
+    fastcgi_param SOGO_AUTH_INTERNAL $sogo_auth_internal;
     fastcgi_read_timeout 3600;
     fastcgi_send_timeout 3600;
 }