refactor : simplify codebase and fix critical issues

Backend:
- Add MCP Serializer to centralize entity-to-array conversion (~300 lines deduped)
- Fix race condition in task/ticket number generation (SELECT FOR UPDATE + transaction)
- Add unique constraint on task (project_id, number) with migration
- Fix MIME type validation: use server-detected finfo instead of client-supplied type
- Add allowlist of permitted MIME types for uploads
- Fix TaskDocumentDownloadController: allow ROLE_CLIENT access, add priority:1
- Fix notification sent even when ticket status unchanged
- Remove redundant exception constructors
- Simplify services (BookStackApi double fetch, TokenEncryptor, GiteaApi)
- Consolidate duplicate checks in processors

Frontend:
- Fix useApi isHandlingUnauthorized scope (module-level to prevent double 401 redirect)
- Fix client-tickets toast key copy-paste bug
- Merge duplicated tasks service methods (getByProject + getByProjectArchived)
- Extract shared uploadWithRelation helper in task-documents service
- Extract formatFileSize utility from duplicated component code
- Extract status transition logic into useClientTicketHelpers composable
- Remove dead code (unused router, handleLogout, empty script blocks)
- Merge duplicate watchers and onMounted calls
- Normalize arrow functions to function declarations per convention

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/State/TaskNumberProcessor.php

@@ -9,6 +9,7 @@ use ApiPlatform\Metadata\Post;
 use ApiPlatform\State\ProcessorInterface;
 use App\Entity\Task;
 use App\Repository\TaskRepository;
+use Doctrine\ORM\EntityManagerInterface;
 use Symfony\Component\DependencyInjection\Attribute\Autowire;
 
 /**
@@ -23,6 +24,7 @@ final readonly class TaskNumberProcessor implements ProcessorInterface
         #[Autowire(service: 'api_platform.doctrine.orm.state.persist_processor')]
         private ProcessorInterface $persistProcessor,
         private TaskRepository $taskRepository,
+        private EntityManagerInterface $entityManager,
     ) {}
 
     /**
@@ -31,8 +33,12 @@ final readonly class TaskNumberProcessor implements ProcessorInterface
     public function process(mixed $data, Operation $operation, array $uriVariables = [], array $context = []): mixed
     {
         if ($operation instanceof Post && null !== $data->getProject()) {
-            $maxNumber = $this->taskRepository->findMaxNumberByProject($data->getProject());
-            $data->setNumber($maxNumber + 1);
+            return $this->entityManager->wrapInTransaction(function () use ($data, $operation, $uriVariables, $context) {
+                $maxNumber = $this->taskRepository->findMaxNumberByProjectForUpdate($data->getProject());
+                $data->setNumber($maxNumber + 1);
+
+                return $this->persistProcessor->process($data, $operation, $uriVariables, $context);
+            });
         }
 
         return $this->persistProcessor->process($data, $operation, $uriVariables, $context);