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/zh.ts

@@ -474,6 +474,7 @@ export const zhTranslation = {
     userMgmtLibrariesValidation: '请至少选择一个音乐库。',
     userMgmtLibrariesUpdateError: '用户已保存，但音乐库分配失败',
     userMgmtNoLibraries: '未分配音乐库',
+    userMgmtNeverSeen: '从未',
     userMgmtSave: '保存',
     userMgmtCancel: '取消',
     userMgmtDelete: '删除',