grafana: capture demo dashboard state; 10s build-info scrape

Overview: echarts readouts for latency/loss/ingress/egress with logo-derived
trace colours, native pill cells for QoS/QoE/Status, LIVE vs DONE computed
from the time window, stable top-10 subscriptions graph, full-resolution
peak queries, placeholder media attributes derived from track names.
prometheus: scrape /info at 10s so the version badge tracks a redeploy.

Author: gmarzot