feat(catalog) : add admin categories page with MalioDataTable and drawer (first draft)

- Page Nuxt /admin/categories : MalioDataTable + bouton Ajouter
- CategoryDrawer : modes creation / consultation / edition (transition
  auto view -> edit a la 1re modif), validation client RG-1.02/04/05,
  mapping erreurs server 409 (doublon) et 422 (violations)
- CategoryDeleteModal : confirmation suppression (soft delete cote API)
- Types Category, CategoryType, User
- i18n admin.categories.* (titre, table, form, validation, toasts)
- Fix latent : ajout 'categories' a AdminLinkSlug e2e (oubli ERP-47)

Logique fetch inline volontaire au M0 — extraction en composables a
ERP-50 (ticket 0.8). Aucune persistance d'etat de tableau dans l'URL.

frontend/tests/e2e/helpers/pages/SidebarComponent.ts

@@ -1,6 +1,6 @@
 import type { Locator, Page } from '@playwright/test'
 
-export type AdminLinkSlug = 'users' | 'roles' | 'sites' | 'audit-log'
+export type AdminLinkSlug = 'users' | 'roles' | 'sites' | 'categories' | 'audit-log'
 
 /**
  * Page Object de la sidebar (MalioSidebar), scope sur les items "admin".