feat: admin audit logging across all admin actions

- AdminLogger: JSON-lines → /var/log/xamxam.log (prod) / storage/logs/admin.log (dev)
  + best-effort DB mirror to admin_audit_log table
- DB: admin_audit_log table, share_links.is_archived column
- ShareLink: archive() replaces delete(), toggleActive() returns new state,
  listActive()/listArchived() split, validateLink blocks archived slugs
- All action handlers wired: publish, unpublish, visibility, delete, csv/db export,
  tfe add/edit, tags, pages, apropos, form-help, access-request, maintenance,
  settings (formulaire toggles, objet types, smtp update), smtp-test
- acces.php: archive button replaces delete; collapsible archived links section
- setup-server.sh: provision /var/log/xamxam.log (www-data:xamxam 640)

app/public/admin/actions/maintenance.php

@@ -10,15 +10,19 @@ if ($_SERVER['REQUEST_METHOD'] !== 'POST'
     die("Accès refusé.");
 }
 
+require_once APP_ROOT . '/src/AdminLogger.php';
+
 $action = $_POST['action'] ?? '';
 
 if ($action === 'enable_maintenance') {
     file_put_contents(MAINTENANCE_FLAG, date('c'));
+    AdminLogger::make()->logMaintenance(true);
     App::flash('success', "Mode maintenance activé.");
 } elseif ($action === 'disable_maintenance') {
     if (file_exists(MAINTENANCE_FLAG)) {
         unlink(MAINTENANCE_FLAG);
     }
+    AdminLogger::make()->logMaintenance(false);
     App::flash('success', "Mode maintenance désactivé.");
 } else {
     App::flash('error', "Action inconnue.");