The per-agent terminal marks turn boundaries (◆ TURN ← / ✓ turn) but
shows no time. Append a wall-clock HH:MM:SS to both the turn-start and
turn-end rows, plus the elapsed duration on turn-end, rendered as dim
metadata so the boundary glyph stays the focus.
This is the frontend half of the feature; it reads a per-event `ts`
(unix seconds) off the turn_start / turn_end events. The read is guarded
on a numeric `ts`, so until the harness surfaces per-event timestamps
the rows render exactly as before (inert-until-capture). Once the
backend attaches `ts` to the history rows + live SSE frame, the times
light up automatically for both live and scrollback, with no further
frontend change.
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