ECDSA P-256 route certificate and session proof verification ported from
CultMeshAuthorityProof.cs using the p256 crate (new dependency, pure Rust,
no default features), judged against the shared contracts/cultmesh vectors.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
ECDSA P-256 route certificate and session proof verification ported from
CultMeshAuthorityProof.cs, with typed refusals, judged against the shared
contracts/cultmesh authority route vectors (C# written and TS signed).
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>