feat : add maintenance mode toggle in admin panel

- Backend: MaintenanceModeListener blocks non-admin API requests when
  var/maintenance flag file exists. MaintenanceController provides
  toggle (PUT /api/admin/maintenance) and public check endpoint
  (GET /api/maintenance/check).
- Frontend: Toggle button in admin page, maintenance.vue page for
  blocked users, middleware redirects non-admins to /maintenance.

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

src/Controller/MaintenanceController.php

@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Controller;
+
+use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpKernel\KernelInterface;
+use Symfony\Component\Routing\Attribute\Route;
+
+final class MaintenanceController extends AbstractController
+{
+    public function __construct(
+        private readonly KernelInterface $kernel,
+    ) {}
+
+    #[Route('/api/maintenance/check', name: 'maintenance_check', methods: ['GET'])]
+    public function check(): JsonResponse
+    {
+        return new JsonResponse([
+            'enabled' => file_exists($this->flagPath()),
+        ]);
+    }
+
+    #[Route('/api/admin/maintenance', name: 'admin_maintenance_status', methods: ['GET'])]
+    public function status(): JsonResponse
+    {
+        $this->denyAccessUnlessGranted('ROLE_ADMIN');
+
+        return new JsonResponse([
+            'enabled' => file_exists($this->flagPath()),
+        ]);
+    }
+
+    #[Route('/api/admin/maintenance', name: 'admin_maintenance_toggle', methods: ['PUT'])]
+    public function toggle(): JsonResponse
+    {
+        $this->denyAccessUnlessGranted('ROLE_ADMIN');
+
+        $path = $this->flagPath();
+
+        if (file_exists($path)) {
+            unlink($path);
+            $enabled = false;
+        } else {
+            file_put_contents($path, (string) time());
+            $enabled = true;
+        }
+
+        return new JsonResponse(['enabled' => $enabled]);
+    }
+
+    private function flagPath(): string
+    {
+        return $this->kernel->getProjectDir() . '/var/maintenance';
+    }
+}

src/EventListener/MaintenanceModeListener.php

@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\EventListener;
+
+use Symfony\Component\EventDispatcher\Attribute\AsEventListener;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpKernel\Event\RequestEvent;
+use Symfony\Component\HttpKernel\KernelInterface;
+use Symfony\Component\Security\Core\Authentication\Token\Storage\TokenStorageInterface;
+
+#[AsEventListener(event: 'kernel.request', priority: 10)]
+final class MaintenanceModeListener
+{
+    public function __construct(
+        private readonly KernelInterface $kernel,
+        private readonly TokenStorageInterface $tokenStorage,
+    ) {}
+
+    public function __invoke(RequestEvent $event): void
+    {
+        if (!$event->isMainRequest()) {
+            return;
+        }
+
+        $flagFile = $this->kernel->getProjectDir() . '/var/maintenance';
+
+        if (!file_exists($flagFile)) {
+            return;
+        }
+
+        $request = $event->getRequest();
+        $path = $request->getPathInfo();
+
+        // Always allow maintenance status endpoint and session endpoints
+        if (str_starts_with($path, '/api/admin/maintenance')
+            || str_starts_with($path, '/api/maintenance/check')
+            || str_starts_with($path, '/api/session')
+            || str_starts_with($path, '/api/health')
+            || str_starts_with($path, '/api/docs')
+        ) {
+            return;
+        }
+
+        // Allow admin users through
+        $token = $this->tokenStorage->getToken();
+        if ($token && $token->getUser()) {
+            $roles = $token->getRoleNames();
+            if (in_array('ROLE_ADMIN', $roles, true)) {
+                return;
+            }
+        }
+
+        $event->setResponse(new JsonResponse(
+            ['message' => 'Application en maintenance. Veuillez réessayer ultérieurement.'],
+            JsonResponse::HTTP_SERVICE_UNAVAILABLE,
+        ));
+    }
+}