Adds ledger_hash, validation.full to validation send/receive spans,
and validation_quorum, proposers_validated to consensus.accept spans.
Foundation for Phase 7 ValidationTracker agreement computation.
Part of the external dashboard parity initiative across phases 2-11.
See docs/superpowers/specs/2026-03-30-external-dashboard-parity-design.md
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>