Add tamper-evident audit logging where each entry includes a SHA-256
hash of the previous entry, forming a verifiable chain per mesh.
Events tracked: peer_joined, peer_left, state_set, message_sent
(never logs message content). New WS handlers: audit_query for
paginated retrieval, audit_verify for chain integrity verification.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>