Implement `app/monitoringapi`

[varex83]

Scope

Port charon/app/monitoringapi.go — the HTTP surface that exposes Prometheus metrics, readiness, and liveness probes consumed by the operational layer.

References

• Go: https://github.com/ObolNetwork/charon/blob/main/app/monitoringapi.go
• Tests: monitoringapi_internal_test.go

Acceptance

• Endpoint shape matches Go reference (/metrics, /livez, /readyz)
• Health probes integrate with app/health (Implement app/health #68)
• Tests ported and green
• cargo clippy --workspace --all-targets --all-features -- -D warnings clean

[emlautarom1-agent]

Port audit — app/monitoringapi

• Status: 🔴 not started
• Charon source: app/monitoringapi.go — 252 Go LOC (a file in package app, not a separate package)
• Complexity: Medium — serves Prometheus metrics, pprof, runtime ENR, and /readyz (beacon sync, quorum peers connected, BN version)
• Internal deps: app/eth2wrap✅, app/health (🔴 Implement app/health #68), app/lifecycle, cluster✅, core✅
• Critical path: ⏸ No — observability/liveness surface; depends on Implement app/health #68 health.

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Automated progress audit (2026-06-15). New comment only — no existing issue content was modified.