demo: persist runtime metadata for Grafana dashboards

[armcconnell]

The Grafana demo dashboards are intentionally ClickHouse-only, but some useful headline metrics currently exist only on the parser/bot Prometheus endpoints.

Add ClickHouse persistence for runtime metadata and packet-level parser counters so the dashboards can show them without adding Prometheus.

Desired data:

• parser version and commit on startup
• bot version and commit on startup
• parser process uptime or heartbeat rows
• UDP ingress packets/sec by port/channel
• UDP ingress bytes/sec by port/channel
• parse/frame error counters by channel/reason
• socket client and sink write error counters where useful

Notes:

• Keep top-of-book and depth-of-book dashboards ClickHouse-only.
• Prefer a small append-only runtime metrics/metadata table per feed family, or a shared schema if it stays simple.
• The first dashboard redesign leaves these items out because they are not currently stored in ClickHouse.