Migrate inline styles to CSS classes: error pages, attestation/not_found, register_success, email_verified

- Add reusable CSS classes in app.scss: layout, headings, cards, flash messages, forms, buttons, tables, badges, section headers, dividers
- Migrate 5 templates to use CSS classes instead of inline styles

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

templates/attestation/not_found.html.twig

@@ -3,11 +3,11 @@
 {% block title %}Attestation introuvable - E-Ticket{% endblock %}
 
 {% block body %}
-<div style="max-width:40rem;margin:0 auto;padding:3rem 1rem;">
-    <h1 class="text-3xl font-black uppercase tracking-tighter italic" style="border-bottom:4px solid #111827;display:inline-block;margin-bottom:0.5rem;">Verification attestation</h1>
+<div class="page-container-md">
+    <h1 class="text-3xl font-black uppercase tracking-tighter italic heading-page">Verification attestation</h1>
 
-    <div style="border:4px solid #991b1b;box-shadow:6px 6px 0 rgba(0,0,0,1);background:#fee2e2;padding:1.5rem;margin-top:2rem;">
-        <p class="font-black text-sm" style="margin-bottom:0.5rem;color:#991b1b;">Attestation introuvable</p>
+    <div class="card-brutal-error mt-8">
+        <p class="font-black text-sm mb-2 text-red-800">Attestation introuvable</p>
         <p class="text-sm text-gray-700">Ce document ne correspond a aucun virement enregistre dans notre systeme. Il est possible que l'attestation ait ete alteree ou falsifiee.</p>
     </div>
 </div>