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/Service/NotificationService.php

@@ -52,12 +52,12 @@ final readonly class NotificationService
             return;
         }
 
-        $number      = sprintf('CT-%03d', $ticket->getNumber());
-        $statusLabel = $ticket->getStatus();
-        $message     = 'Nouveau statut : '.$statusLabel;
+        $number        = sprintf('CT-%03d', $ticket->getNumber());
+        $statusComment = $ticket->getStatusComment();
+        $message       = 'Nouveau statut : '.$ticket->getStatus();
 
-        if (null !== $ticket->getStatusComment() && '' !== $ticket->getStatusComment()) {
-            $message .= ' — '.$ticket->getStatusComment();
+        if (null !== $statusComment && '' !== $statusComment) {
+            $message .= ' — '.$statusComment;
         }
 
         $notification = new Notification();