First slice of #1424 (per-agent /stats enrichments):
- Backend: add per-bucket result_counts to the stats Snapshot (mirrors
model_counts), so result outcomes can be charted over time, not just
as a window total.
- Frontend: two new summary chips — cache hit-rate % (cached input vs
all input-side tokens) and avg tokens/turn — both derived from the
existing per-bucket token sums. Plus a stacked result-trend chart so
error / rate-limit / compaction spikes are visible across the window.
Hive-wide aggregate, cost estimate, and container resource load land in
follow-up PRs.
ded7474b2b