Extract last 3 inline styles from admin templates into CSS classes

admin/thanks.php:
- <div style="margin-top:1.5rem;display:flex;gap:.75rem;flex-wrap:wrap;"> → class="admin-action-bar"
- <p style="color:var(--text-secondary);"> → class="admin-muted"

admin/pages.php:
- Éditer button style="font-size:.8rem;padding:.3rem .75rem;" → class="admin-btn admin-btn--sm"

admin.css (Thesis info sections block):
- Added .admin-action-bar { margin-top:1.5rem; display:flex; gap:0.75rem; flex-wrap:wrap }
- Added .admin-muted { color: var(--text-secondary) }

The only remaining inline style in any admin PHP file is the dynamic
--disk-pct/--disk-color custom properties on the disk bar in system.php,
which carry PHP runtime values and cannot be moved to static CSS.

public/admin/pages.php

@@ -42,7 +42,7 @@ try {
                 <td><?= htmlspecialchars($p['updated_at'] ?? '—') ?></td>
                 <td>
                     <a href="/admin/pages-edit.php?slug=<?= urlencode($p['slug']) ?>"
-                       class="admin-btn" style="font-size:.8rem;padding:.3rem .75rem;">Éditer</a>
+                       class="admin-btn admin-btn--sm">Éditer</a>
                 </td>
             </tr>
             <?php endforeach; ?>

public/admin/thanks.php

@@ -138,14 +138,14 @@ $pageTitle = "Récapitulatif TFE";
         </section>
         <?php endif; ?>
 
-        <div style="margin-top:1.5rem;display:flex;gap:.75rem;flex-wrap:wrap;">
+        <div class="admin-action-bar">
             <a href="/admin/edit.php?id=<?= $thesisId ?>" class="admin-btn">Modifier</a>
             <a href="/admin/add.php" class="admin-btn-secondary">Ajouter un autre TFE</a>
             <a href="/admin/" class="admin-btn-secondary">Retour à la liste</a>
         </div>
 
     <?php else: ?>
-        <p style="color:var(--text-secondary);">Aucune donnée à afficher.</p>
+        <p class="admin-muted">Aucune donnée à afficher.</p>
         <p><a href="/admin/add.php" class="admin-btn-secondary">Retour au formulaire</a></p>
     <?php endif; ?>
 </main>

public/assets/css/admin.css

@@ -622,6 +622,17 @@
   font-size: 0.9rem;
 }
 
+.admin-action-bar {
+  margin-top: 1.5rem;
+  display: flex;
+  gap: 0.75rem;
+  flex-wrap: wrap;
+}
+
+.admin-muted {
+  color: var(--text-secondary);
+}
+
 /* ── Section titles (account, etc.) ─────────────────────────────────────── */
 .admin-section-title {
   font-size: 1rem;