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>

frontend/services/tasks.ts

@@ -10,18 +10,10 @@ export function useTaskService() {
         return extractHydraMembers(data)
     }
 
-    async function getByProject(projectId: number): Promise<Task[]> {
+    async function getByProject(projectId: number, archived = false): Promise<Task[]> {
         const data = await api.get<HydraCollection<Task>>('/tasks', {
             project: `/api/projects/${projectId}`,
-            archived: false,
-        })
-        return extractHydraMembers(data)
-    }
-
-    async function getByProjectArchived(projectId: number): Promise<Task[]> {
-        const data = await api.get<HydraCollection<Task>>('/tasks', {
-            project: `/api/projects/${projectId}`,
-            archived: true,
+            archived,
         })
         return extractHydraMembers(data)
     }
@@ -49,5 +41,5 @@ export function useTaskService() {
         })
     }
 
-    return { getAll, getByProject, getByProjectArchived, getFiltered, create, update, remove }
+    return { getAll, getByProject, getFiltered, create, update, remove }
 }