refactor(backend): normalize naming convention to backend rather storage

no ambiguity with the backend rather storage

frontend/static/locales/en.json

@@ -1121,7 +1121,7 @@
     "storage_size": "Stored",
     "storage_tab": "Storage",
     "storage_test": "Test",
-    "storage_backend_audit": "Storage consistency",
+    "storage_backend_audit": "Backend consistency",
     "storage_backend_audit_triggered": "backend_consistency triggered for `{{name}}` — watch it on the Jobs tab.",
     "time_day_ago": "{{n}} d ago",
     "time_hour_ago": "{{n}} h ago",

frontend/static/locales/fr.json

@@ -779,7 +779,7 @@
     "storage_path_style": "Forcer le style de chemin",
     "storage_path_style_hint": "Requis pour MinIO et certains services compatibles S3",
     "storage_test": "Test",
-    "storage_backend_audit": "Cohérence du stockage",
+    "storage_backend_audit": "Cohérence du backend",
     "storage_backend_audit_triggered": "backend_consistency lancé pour `{{name}}` — suivez son avancement dans l’onglet Tâches.",
     "storage_test_connection": "Tester la connexion",
     "storage_test_success": "Connexion réussie",