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/api/navidromeAdmin.ts

@@ -13,6 +13,7 @@ export interface NdUser {
   isAdmin: boolean;
   libraryIds: number[];
   lastLoginAt?: string | null;
+  lastAccessAt?: string | null;
   createdAt?: string;
   updatedAt?: string;
 }
@@ -56,6 +57,7 @@ export async function ndListUsers(serverUrl: string, token: string): Promise<NdU
       isAdmin: !!o.isAdmin,
       libraryIds: extractLibraryIds(o),
       lastLoginAt: (o.lastLoginAt as string | null | undefined) ?? null,
+      lastAccessAt: (o.lastAccessAt as string | null | undefined) ?? null,
       createdAt: o.createdAt as string | undefined,
       updatedAt: o.updatedAt as string | undefined,
     };