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/ClientTicketNumberProcessor.php

@@ -51,12 +51,13 @@ final readonly class ClientTicketNumberProcessor implements ProcessorInterface
             }
         }
 
-        $nextNumber = $this->clientTicketRepository->findNextNumberForProject($project);
-        $data->setNumber($nextNumber);
+        $now = new DateTimeImmutable();
+
+        $data->setNumber($this->clientTicketRepository->findNextNumberForProjectForUpdate($project));
         $data->setSubmittedBy($user);
         $data->setStatus('new');
-        $data->setCreatedAt(new DateTimeImmutable());
-        $data->setUpdatedAt(new DateTimeImmutable());
+        $data->setCreatedAt($now);
+        $data->setUpdatedAt($now);
 
         $this->entityManager->persist($data);
         $this->entityManager->flush();