feat(users): show last-access timestamp per user

Maps Navidrome's lastAccessAt onto NdUser and renders it in the
User Management row as a localized relative time (Intl.RelativeTimeFormat
with the current i18n language). Tooltip carries the absolute
timestamp. Navidrome returns 0001-01-01 for never-accessed users —
detected and shown as the localized "Never" label.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/locales/fr.ts

@@ -479,6 +479,7 @@ export const frTranslation = {
     userMgmtLibrariesValidation: 'Sélectionnez au moins une bibliothèque.',
     userMgmtLibrariesUpdateError: 'Utilisateur enregistré, mais l\u2019attribution des bibliothèques a échoué',
     userMgmtNoLibraries: 'Aucune bibliothèque attribuée',
+    userMgmtNeverSeen: 'Jamais',
     userMgmtSave: 'Enregistrer',
     userMgmtCancel: 'Annuler',
     userMgmtDelete: 'Supprimer',