feat: render flash messages as toasts

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

templates/_partials/_flashes.html.twig

@@ -1,12 +1,10 @@
-{# Just the alerts. The positioned container with id="flashes" lives in layout.html.twig, because
-   that is the element htmx swaps out of band after a booking. Flat inline alerts for now: myep
-   renders these as Toastify toasts, which would mean adopting toastify-js (plan step 2/7). #}
-{% set levels = { error: 'bg-red-600', warning: 'bg-amber-600', success: 'bg-emerald-600', info: 'bg-primary' } %}
+{# Just the toast triggers. The container with id="flashes" lives in layout.html.twig, because
+   that is the element htmx swaps out of band after a booking. Each element is empty: the
+   toast_controller hands the message to Toastify, which renders it at the top right. #}
+{% set levels = ['error', 'warning', 'success', 'info'] %}
 
-{% for level, messages in app.flashes(levels|keys) %}
+{% for level, messages in app.flashes(levels) %}
     {% for message in messages %}
-        <div class="{{ levels[level] }} text-white rounded shadow-lg px-4 py-3 text-sm">
-            {{ message|trans }}
-        </div>
+        <div {{ stimulus_controller('toast', { text: message|trans, class: 'toastify--' ~ level }) }}></div>
     {% endfor %}
 {% endfor %}