SEC-001: MmapGradientAccumulator now uses checked arithmetic for all
offset computations, validates node_id bounds before pointer ops, and
asserts mmap bounds before read/write. Matches MmapManager's safe pattern.
SEC-002: ProofAttestation hashes are now computed over actual proof and
environment content using domain-separated SipHash-2-4, filling all 32
bytes. Replaces the previous scheme that left 24+ bytes as zeros and used
only counter values. Removes false Ed25519 claim from module docs.
Also fixes ruvector-verified CI: unused_mut warnings in ruvector-core
(feature-gated code) and clippy unnecessary_lazy_evaluations in lib.rs.
Co-Authored-By: claude-flow <ruv@ruv.net>