chore(grafana): rebase Morph dashboard on upstream reth and add proofs-history panels

[panos-xyz]

Background

etc/grafana/dashboards/morph-reth.json is a Morph fork of upstream reth's overview dashboard, plus Morph-specific Engine API / payload-builder rows. The last dashboard change in this repo was PR #110 (2026-05-20, "Improve Grafana dashboard signal quality"). Since then we have stayed on reth v2.4.0 while upstream's etc/grafana/dashboards/overview.json continued to grow (state-root task, proof workers, engine-API message mix, blob/getBlobs latency, cargo-features, etc.). The Morph JSON was never rebased onto that tree.

Separately, bounded historical proofs (PR #142 / proofs-history ExEx) already emit Prometheus metrics that have no dashboard coverage:

• morph.proofs: per-block duration (total / execution / state-root / write), trie/leaf write counters, earliest_block / latest_block window gauges, prune and unwind error counters.
• morph.rpc.proofs: eth_getProof request / success / failure counters and latency.

Operators therefore cannot see whether the 7-day proofs window is healthy, lagging, pruning, or serving RPC, from the provisioned Grafana stack (etc/docker-compose.yml).

Problem

1. Drift from upstream. Broken or stale PromQL against current reth metric names; missing panels that operators already expect from a v2.4 reth node.
2. No proofs-history observability. After enabling --morph.proofs-history, there is no row for window bounds, catch-up cost, prune/unwind failures, or historical-proof RPC rate/latency.

Proposed work

1. Rebase etc/grafana/dashboards/morph-reth.json onto the upstream reth overview dashboard that matches our pinned tag (paradigmxyz/reth v2.4.0), then re-apply Morph-only rows (custom L2 Engine API, payload builder, head timegap, Morph filters chain / role / service). Do not blindly copy later-than-v2.4 panels whose metric names we do not emit yet.
2. Keep the Morph-specific Engine API and payload-builder sections; they are not in upstream.
3. Add a Proof History row covering at least:
   • Window: reth_morph_proofs_earliest_block / reth_morph_proofs_latest_block (and the gap vs canonical height).
   • Ingest cost: block_total_duration_seconds, block_execution_duration_seconds, block_state_root_duration_seconds, block_write_duration_seconds.
   • Write volume: account/storage trie updates and hashed leaves.
   • Errors: prune_errors_total, unwind_errors_total.
   • RPC: reth_morph_rpc_proofs_requests_total, success/failure rates, latency_seconds.
4. Follow the export flow in etc/README.md (Grafana UI export for sharing externally) so the JSON stays importable by etc/docker-compose.yml provisioning. Preserve ${datasource} / Prometheus placeholder replacement.
5. Short note in etc/README.md that proofs-history panels require the node to be run with proofs history enabled.

Out of scope

• Changing metric names in morph-proofs / morph-rpc (adapt the dashboard to what we already emit).
• Alerting rules / Grafana Cloud.
• Implementing eth_getMultiProof (separate issue). If that RPC lands first, add a method label or a second RPC series in the same Proof History row.

Acceptance

• Dashboard still provisions from etc/grafana and the Morph Engine / payload rows still work.
• New Proof History panels render against a node that has proofs history on (empty/zero is fine when it is off).
• PromQL uses metrics that exist on the v2.4.0 + Morph binary; no panels pointed at names we do not scrape.