feat(mail) : MailFoldersListController - GET /api/mail/folders (arbre BDD + unreadCount)

- lit la BDD (pas l'IMAP live), retourne l'arbre des dossiers avec metadata
- securite via MailAccessChecker : ROLE_USER/ADMIN, refus ROLE_CLIENT pur
- tests fonctionnels 401/403/200

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Functional/Controller/Mail/MailFoldersControllerTest.php

@@ -0,0 +1,50 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Functional\Controller\Mail;
+
+use App\Entity\User;
+use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;
+
+/**
+ * @internal
+ */
+class MailFoldersControllerTest extends WebTestCase
+{
+    public function testListFoldersReturns401WhenNotAuthenticated(): void
+    {
+        $client = static::createClient();
+        $client->request('GET', '/api/mail/folders');
+
+        self::assertResponseStatusCodeSame(401);
+    }
+
+    public function testListFoldersReturns403ForRoleClient(): void
+    {
+        $client    = static::createClient();
+        $container = static::getContainer();
+        $em        = $container->get('doctrine.orm.entity_manager');
+
+        $clientUser = $em->getRepository(User::class)->findOneBy(['username' => 'client-liot']);
+        $client->loginUser($clientUser);
+        $client->request('GET', '/api/mail/folders');
+
+        self::assertResponseStatusCodeSame(403);
+    }
+
+    public function testListFoldersReturns200ForRoleUser(): void
+    {
+        $client    = static::createClient();
+        $container = static::getContainer();
+        $em        = $container->get('doctrine.orm.entity_manager');
+
+        $user = $em->getRepository(User::class)->findOneBy(['username' => 'alice']);
+        $client->loginUser($user);
+        $client->request('GET', '/api/mail/folders');
+
+        self::assertResponseIsSuccessful();
+        $data = json_decode($client->getResponse()->getContent(), true);
+        self::assertIsArray($data);
+    }
+}