feat(mail) : migrate Mail integration into module (back)

LST-67 (2.5) backend. Behaviour-preserving move of the IMAP mail integration
into src/Module/Mail/. All /api/mail/* routes, securities (ROLE_CLIENT still
excluded via MailAccessChecker) and the async sync are unchanged.

- 4 entities + 4 repositories (Domain interfaces + Doctrine impls, bound).
  TaskMailLink.task now references TaskInterface (contract) instead of the
  concrete PM Task. Link/unlink/list-mails controllers load tasks via
  TaskRepositoryInterface; MailCreateTaskController keeps the concrete Task
  (instantiation) — documented Mail->PM coupling.
- Domain (MailProviderInterface, exception), Application (5 DTOs, MailSyncService,
  MailSyncRequested message + handler), Infrastructure (ImapMailProvider +
  MimeHeaderDecoder, MailAccessChecker, 2 console commands, 12 controllers,
  ApiPlatform state + MailSettings resource). TokenEncryptor stays shared.
- doctrine mapping Mail; messenger routing repointed; services.yaml repo +
  provider bindings; MailModule registered (id mail, mail.access/configure).
- #[Auditable] + Timestampable on MailConfiguration only (additive migration);
  IMAP data entities keep their own sync timestamps.

163 tests green, mapping valid, no route regression, cs-fixer clean.

tests/Functional/Controller/Mail/MailTaskIntegrationControllerTest.php

@@ -4,9 +4,9 @@ declare(strict_types=1);
 
 namespace App\Tests\Functional\Controller\Mail;
 
-use App\Entity\MailFolder;
-use App\Entity\MailMessage;
 use App\Module\Core\Domain\Entity\User;
+use App\Module\Mail\Domain\Entity\MailFolder;
+use App\Module\Mail\Domain\Entity\MailMessage;
 use App\Module\ProjectManagement\Domain\Entity\Project;
 use App\Module\ProjectManagement\Domain\Entity\Task;
 use DateTimeImmutable;