fix(errors) : humanize backend error messages for end users

Add centralized error translation layer (humanizeError) that converts
raw Symfony/Doctrine/API Platform messages into user-friendly French.
Fix useApi to extract errors from all backend response formats
(violations, error, message, hydra:description, detail).
Add toast deduplication to prevent double display. Replace error toast
icon (X → CircleX) to distinguish from the dismiss button.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/pages/machine-skeleton/index.vue

@@ -104,6 +104,7 @@
 import { ref, computed, onMounted } from "vue";
 import { useMachineTypesApi } from "~/composables/useMachineTypesApi";
 import { useToast } from "~/composables/useToast";
+import { humanizeError } from "~/shared/utils/errorMessages";
 import IconLucidePlus from "~icons/lucide/plus";
 import IconLucidePackage from "~icons/lucide/package";
 import IconLucideLayoutGrid from "~icons/lucide/layout-grid";
@@ -148,10 +149,10 @@ const confirmDeleteType = async (type) => {
       if (result.success) {
         showSuccess(`Type "${type.name}" supprimé avec succès`);
       } else {
-        showError(`Erreur lors de la suppression: ${result.error}`);
+        showError(`Impossible de supprimer le type : ${result.error}`);
       }
     } catch (error) {
-      showError(`Erreur lors de la suppression: ${error.message}`);
+      showError(`Impossible de supprimer le type : ${humanizeError(error.message)}`);
     }
   }
 };