feat(mail) : install symfony/messenger + browser-kit + ENCRYPTION_KEY test (deps Phase 3)

- ajoute symfony/messenger ^8.0 et symfony/doctrine-messenger ^8.0 pour la sync mail async
- ajoute symfony/browser-kit + css-selector en dev pour tests fonctionnels WebTestCase
- ENCRYPTION_KEY ajoutee dans phpunit.dist.xml pour permettre le chiffrement en test
- MESSENGER_TRANSPORT_DSN configure (Doctrine), messenger.yaml minimal (sera enrichi en Task 12)
- fix(orm) : ClientTicket - migre uniqueConstraints en attribut separe (Doctrine ORM 4 deprecation)

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

src/Entity/ClientTicket.php

@@ -47,12 +47,8 @@ use Symfony\Component\Validator\Constraints as Assert;
     order: ['createdAt' => 'DESC'],
 )]
 #[ORM\Entity(repositoryClass: ClientTicketRepository::class)]
-#[ORM\Table(
-    name: 'client_ticket',
-    uniqueConstraints: [
-        new ORM\UniqueConstraint(name: 'uniq_client_ticket_project_number', columns: ['project_id', 'number']),
-    ],
-)]
+#[ORM\Table(name: 'client_ticket')]
+#[ORM\UniqueConstraint(name: 'uniq_client_ticket_project_number', columns: ['project_id', 'number'])]
 class ClientTicket
 {
     public const string TYPE_BUG         = 'bug';