Implement `cmd/addvalidators`

[varex83]

Scope

Port charon/cmd/addvalidators.go (~255 LOC) — the pluto addvalidators command that adds validators to an existing cluster.

References

• Go: https://github.com/ObolNetwork/charon/blob/main/cmd/addvalidators.go
• Tests: cmd/addvalidators_internal_test.go (~441 LOC)

Acceptance

• Flag/help parity with charon
• Tests ported and green
• cargo clippy --workspace --all-targets --all-features -- -D warnings clean

[emlautarom1-agent]

Port audit — cmd/addvalidators

• Status: 🔴 not started — unblocked
• Charon source: cmd/addvalidators.go — 188 non-test Go LOC (696 total)
• Complexity: Complex — adds validators to an existing cluster via a cluster mutation, generating deposit data + keystores
• Internal deps: app, cluster✅, dkg ✅ (feat: dkg #373), eth2util/deposit✅, eth2util/keystore✅, tbls✅
• Critical path: independent of cmd/run; deps already merged (dkg + cluster mutation mutationaddvalidator.rs exists), so this can start now.

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