Instance details: history payload fields (state, end time, duration) are fetched but never displayed

[javahippie]

Summary

The instance details description renders only the instance id and the business key — in history mode, the richer historic payload (state, start/end time, duration) is fetched but never displayed. Toggling history mode therefore changes nothing visible in the details header, even after the stale-refetch bug (#94) is fixed.

Current state (src/pages/Processes.jsx, InstanceDetailsDescription)

<dl>
  <dt>…instance-id…</dt><dd>{data?.id ?? "—"}</dd>
  <dt>…business-key…</dt><dd>{data?.businessKey ?? "—"}</dd>
</dl>

GET /history/process-instance/{id} additionally returns state (ACTIVE, COMPLETED, EXTERNALLY_TERMINATED, …), startTime, endTime, durationInMillis, startUserId, deleteReason — all discarded.

Suggested implementation

Extend the description list, rendering history-only fields when present (they are simply absent in the runtime payload, so no mode switch is needed in the component):

• State (badge-style, e.g. COMPLETED)
• Start time / end time (<time> elements, as in the instance list)
• Duration (humanized from durationInMillis)
• Started by (startUserId), delete reason if set

This complements #94 (refetch on toggle), #99 (diagram) and #100 (activity history) — together they make history mode visibly different from the live view.