Fuzzer: Dashboard panel for fuzz run metrics

[LeJamon]

Goal

Surface fuzz run metrics (txs submitted / succeeded / failed, divergences, ledger comparisons, mutations) in the existing xrpl-confluence dashboard so operators can see progress in real time instead of only via /status polling.

Why

Today the sidecar exposes /status returning the runners.Stats JSON. The dashboard (xrpl-confluence/dashboard/) already renders per-node health for rippled/goxrpl; a fuzz panel would show:

• Current state (running / completed)
• Counters over time (txs_submitted, divergences — sparklines)
• Last-observed divergence kind + timestamp
• Seed (so you can copy-paste for a reproduce run)

Approach sketch

• Optional: add a Prometheus-compatible metrics endpoint (/metrics) using github.com/prometheus/client_golang.
• Dashboard scrapes or polls /status (simpler: matches the existing pattern).
• New dashboard panel: reads /status every few seconds, renders sparklines + a status tile.

Prerequisites

None — stats already exist in runners.Stats across all three modes (fuzz / replay / reproduce).

Deliverables

• Optional Prometheus metrics on sidecar
• Dashboard JS/HTML additions under xrpl-confluence/dashboard/
• Screenshot / quick demo in the PR description