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/components/admin/AdminBookStackTab.vue

@@ -10,15 +10,13 @@
                 input-class="w-full"
             />
 
-            <div>
-                <MalioInputText
-                    v-model="form.tokenId"
-                    :label="$t('bookstack.settings.tokenId')"
-                    :placeholder="$t('bookstack.settings.tokenIdPlaceholder')"
-                    input-class="w-full"
-                    type="password"
-                />
-            </div>
+            <MalioInputText
+                v-model="form.tokenId"
+                :label="$t('bookstack.settings.tokenId')"
+                :placeholder="$t('bookstack.settings.tokenIdPlaceholder')"
+                input-class="w-full"
+                type="password"
+            />
 
             <div>
                 <MalioInputText