[Studio][Bug] User management renders UTC session timestamps as browser-local time

Start with UserManagement.tsx and the shared format.ts helper, then compare the alert and query-history fixes referenced in the issue. Trace the dateTime helper through the user-management table and CSV export; done means all listed timestamps render and export with the same UTC conversion and local display as those other pages.

Problem

The Studio user management page renders lastSessionSeenAt,
earestSessionExpiresAt, passwordChangedAt, gmtCreate, and gmtModified with
ew Date(value).toLocaleString(). Those values are offset-less \LocalDateTime\ strings. JavaScript therefore treats them as browser-local wall-clock times, so every viewer outside UTC sees session activity and password-change times shifted by their UTC offset.

Evidence

• \AuthService.now()\ (\server/src/main/java/org/apache/rocketmq/studio/auth/AuthService.java) writes \LocalDateTime.ofInstant(Instant.ofEpochMilli(clock.millis()), ZoneOffset.UTC)\ into session \last_seen_at\ / \expires_at\ and user \password_changed_at. The clock is \Clock.systemUTC().
• \StudioUserVO\ exposes those fields as \LocalDateTime\ (serialized without an offset).
• \UserManagement.tsx\ helper: \const dateTime = (value?: string) => (value ? new Date(value).toLocaleString() : '-');\ used by the table columns 最近活跃 / 最近过期 / 创建时间 and by the CSV export columns.
• Local reproduction (browser TZ \Asia/Shanghai, UTC+8):
  ew Date('2026-08-22T09:30:00').toLocaleString()\ → \2026/8/22 09:30:00\ (wrong; should be 17:30 local).
  ew Date('2026-08-22T09:30:00Z').toLocaleString()\ → \2026/8/22 17:30:00.

The same defect class was already fixed on other surfaces: alert \lastTriggered\ (#4174) and query-history \queriedAt\ (#4221 / #4222). The shared helper \ormatUtcDateTime\ in \web/src/utils/format.ts\ already appends \Z\ for offset-less values; user management never adopted it.

Expected behavior

Render and export these timestamps with \ormatUtcDateTime, matching the alert and query-history pages.

Related

#4174, #4221, #4222