[Studio][Bug] Query history drawer renders UTC timestamps as browser-local time

## Problem

`MessageQueryHistoryDrawer` formats `queriedAt` / `latestQueryAt` with `new Date(value).toLocaleString()`. Backend `QueryHistoryService` stamps those fields with `Clock.systemUTC()` into a `LocalDateTime`, which serializes without a zone offset (`2026-08-05T12:00:00`). The browser therefore treats the value as **local** time and shifts the displayed timestamp by the viewer offset.

This is the same class of bug as the alert rule `lastTriggered` display issue (#4174 / #4199), but on the query-history surface.

## Evidence

- `web/src/components/MessageQueryHistoryDrawer.tsx` `formatTime` uses `toLocaleString()`.
- Backend: `QueryHistoryService` uses `Clock.systemUTC()`; VOs expose `LocalDateTime queriedAt` / `latestQueryAt` with no offset.
- Existing helper: `formatUtcDateTime` in `web/src/utils/format.ts` already appends `Z` for offset-less UTC strings and formats in the viewer timezone.

## Expected behavior

Query history timestamps are rendered as UTC-instant values in the viewer's timezone (via `formatUtcDateTime`), not as browser-local naive datetimes.

## Scope

Frontend drawer formatting + unit test. No API change.

Start in web/src/components/MessageQueryHistoryDrawer.tsx and inspect the formatTime handling for queriedAt and latestQueryAt. Compare it with formatUtcDateTime in web/src/utils/format.ts, then add the requested unit test. Done means offset-less UTC timestamps render as UTC instants in the viewer’s timezone without an API change.

Written by the indexing model from the issue text.