fix(metrics): show turn/step metrics for compacted conversations

Compacted conversations start with a system summary (role: "system")
instead of a user message (role: "user"). The interleaveTurnMetrics
function only detected segments by role === "user", so compacted
conversations got zero segments and no metrics were emitted.

Fix: when no user messages are found but metrics entries exist, treat
the entire transcript as one segment. This places turn-metrics at the
end and anchors step-metrics to any tool-batch groups by stepId.

686 tests green.

0 files changed, 0 insertions, 0 deletions