feat: render flash messages as toasts

Co-Authored-By: Claude Opus 5 <[email protected]>

templates/security/login.html.twig

@@ -18,9 +18,9 @@
                 Mit myep anmelden
             </a>
 
-            <div class="fixed bottom-4 right-4 z-50 space-y-2">
-                {% include '_partials/_flashes.html.twig' %}
-            </div>
+            {# Toastify positions itself, so this needs no wrapper -- and the login page has no
+               board to swap, so it needs no #flashes container either. #}
+            {% include '_partials/_flashes.html.twig' %}
         </div>
     </div>
 {% endblock %}