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/Mcp/Tool/TaskMeta/ListGroupsTool.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace App\Mcp\Tool\TaskMeta;
 
+use App\Mcp\Tool\Serializer;
 use App\Repository\TaskGroupRepository;
 use Mcp\Capability\Attribute\McpTool;
 
@@ -23,17 +24,6 @@ class ListGroupsTool
 
         $groups = $this->taskGroupRepository->findBy($criteria, ['title' => 'ASC']);
 
-        return json_encode(array_map(fn ($g) => [
-            'id'          => $g->getId(),
-            'title'       => $g->getTitle(),
-            'description' => $g->getDescription(),
-            'color'       => $g->getColor(),
-            'project'     => [
-                'id'   => $g->getProject()->getId(),
-                'code' => $g->getProject()->getCode(),
-                'name' => $g->getProject()->getName(),
-            ],
-            'archived' => $g->isArchived(),
-        ], $groups));
+        return json_encode(array_map(Serializer::groupFull(...), $groups));
     }
 }