feat: add constitutional committee endpoints
- /governance/committee: current committee snapshot with members, quorum,
and source NewCommittee governance action (null for the Conway-genesis
committee).
- /governance/committee/votes: paged history of all CC member votes.
- /governance/committee/{cc_id}/votes: paged votes filtered by CIP-129 hot
or cold credential; cold queries aggregate across hot-key rotations.
Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>