feat(helpdesk): Übergabe assignment workflow

- New statuses: under_review
- New DB fields: assigned_to, assigned_by, assigned_at, due_date (migration 012)
- HandoverNotificationService: emails on assign and review-request
- HandoverService: assign(), submitForReview(), resendNotification()
- Assign page: manager selects employee + due date, resend notification
- Create wizard: manager can assign during creation (step 1)
- Edit page: "Submit for review" button for assignee, assign link for manager
- List page: open/closed tabs, non-managers see only their assigned handovers
- Email templates: handover_assigned + handover_review_requested (de/en)
- i18n keys added for de and en

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/helpdesk/lib/Module/Helpdesk/HelpdeskContainerRegistrar.php

@@ -28,8 +28,10 @@ use MintyPHP\Module\Helpdesk\Repository\HandoverRevisionRepository;
 use MintyPHP\Module\Helpdesk\Repository\SoftwareProductRepository;
 use MintyPHP\Module\Helpdesk\Repository\UpdateRepository;
 use MintyPHP\Module\Helpdesk\Service\DomainSecurityLevelService;
+use MintyPHP\Module\Helpdesk\Service\HandoverNotificationService;
 use MintyPHP\Module\Helpdesk\Service\HandoverRevisionService;
 use MintyPHP\Module\Helpdesk\Service\HandoverService;
+use MintyPHP\Service\Mail\MailService;
 use MintyPHP\Module\Helpdesk\Service\UpdateService;
 use MintyPHP\Service\Access\PermissionService;
 use MintyPHP\Service\Settings\SettingServicesFactory;
@@ -142,10 +144,15 @@ final class HelpdeskContainerRegistrar implements ContainerRegistrar
             $c->get(HandoverRepository::class)
         ));
 
+        $container->set(HandoverNotificationService::class, static fn (AppContainer $c): HandoverNotificationService => new HandoverNotificationService(
+            $c->get(MailService::class)
+        ));
+
         $container->set(HandoverService::class, static fn (AppContainer $c): HandoverService => new HandoverService(
             $c->get(HandoverRepository::class),
             $c->get(SoftwareProductService::class),
-            $c->get(HandoverRevisionService::class)
+            $c->get(HandoverRevisionService::class),
+            $c->get(HandoverNotificationService::class)
         ));
 
         $container->set(UpdateRepository::class, static fn (): UpdateRepository => new UpdateRepository());