refactor(catalog) : address Matthieu review on composables (constant + shared helpers)

- useCategoriesAdmin : extract `HYDRA_NO_PAGINATION = 999` to a named
  constant (was duplicated between fetchAll and fetchTypes) + comment
  the post-M0 server-pagination debt.

- useCategoryForm + useApi + shared/utils/api : drop the local copy of
  `extractErrorMessage` in useCategoryForm (it was duplicating the one
  in useApi), and centralize Hydra error / violation extraction in
  `shared/utils/api.ts` via two new helpers :
    - extractApiErrorMessage(data) : tries hydra:description, detail,
      description, message, error, title, hydra:title — used by both
      useApi.onResponseError and useCategoryForm.handleApiError.
    - extractApiViolations(data) : returns the ApiPlatform 422
      violations as a typed array (handles `violations` and
      `hydra:violations`), letting each caller map them onto its own
      fields. useCategoryForm now uses this helper instead of an
      inline loop, ready for the next form drawer to reuse.

handleApiError keeps a manual fallback toast on non-409/422 errors :
the native useApi toast is disabled by design (`toast: false`) to allow
fine-grained 409/422 mapping, so the catch-all branch must re-emit one
or a 500 would be silent.

No behavior change — 43/43 Vitest tests still pass.

config/version.yaml

@@ -1,2 +1,2 @@
 parameters:
-    app.version: '0.1.49'
+    app.version: '0.1.50'

frontend/modules/catalog/components/CategoryDrawer.vue

@@ -7,7 +7,7 @@
         @update:model-value="emit('update:modelValue', $event)"
     >
         <template #header>
-            <h2 class="text-[24px] font-bold">
+            <h2 class="text-2xl font-bold">
                 {{ headerLabel }}
             </h2>
         </template>

frontend/modules/catalog/pages/admin/categories.vue

@@ -13,9 +13,11 @@
             </template>
         </PageHeader>
 
-        <!-- Table des categories : tri par defaut sur Nom ASC (RG-1.10).
-             Tri serveur applique a la requete + pagination front via
-             MalioDataTable (volumetrie cible <= 300, cf. spec § 4.1). -->
+        <!-- Table des categories. Affichage exhaustif (volumetrie cible
+             <= 300, cf. spec § 4.1) — tri 100% serveur via CategoryProvider
+             (name ASC, RG-1.10). La barre de pagination du MalioDataTable
+             reste cosmetique tant qu'aucun slice client n'est cable : a
+             traiter cote @malio/layer-ui le jour ou la volumetrie monte. -->
         <MalioDataTable
             :columns="columns"
             :items="categoryItems"