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>

composer.json

@@ -21,6 +21,7 @@
         "sabre/vobject": "^4.5",
         "symfony/asset": "8.0.*",
         "symfony/console": "8.0.*",
+        "symfony/doctrine-messenger": "^8.0",
         "symfony/dotenv": "8.0.*",
         "symfony/expression-language": "8.0.*",
         "symfony/flex": "^2",
@@ -28,6 +29,7 @@
         "symfony/http-client": "8.0.*",
         "symfony/lock": "8.0.*",
         "symfony/mcp-bundle": "^0.6.0",
+        "symfony/messenger": "^8.0",
         "symfony/mime": "8.0.*",
         "symfony/monolog-bundle": "^4.0",
         "symfony/property-access": "8.0.*",
@@ -95,6 +97,8 @@
     "require-dev": {
         "doctrine/doctrine-fixtures-bundle": "^4.3",
         "friendsofphp/php-cs-fixer": "^3.94",
-        "phpunit/phpunit": "^13.0"
+        "phpunit/phpunit": "^13.0",
+        "symfony/browser-kit": "^8.0",
+        "symfony/css-selector": "^8.0"
     }
 }