Replace AcceptAnyServerCertVerifier (a security hole for X.509) with
verifier selection by PeerEntry presence (ADR-034 §3, OQ-29):
- build_client_auth presents the Ed25519 key as an RFC 7250 raw public
key client cert (replaces with_no_client_auth), activating the
PeerEntry fingerprint -> peer_id resolution path on quinn.
- select_server_verifier: Some(fingerprint) -> FingerprintPinVerifier
(fingerprint match for known peers); None -> WebPkiServerVerifier
(CA verification for public X.509 endpoints). None + Ed25519 raw key
fails closed at handshake (no CA to fall back to).
- FingerprintPinVerifier matches ed25519:<hex> (raw key extraction) and
SHA256:<hex> (DER hash); verifies handshake signatures via
verify_tls13_signature_with_raw_key / verify_tls12/13_signature.
- Extract shared fingerprint logic into alknet_core::fingerprint (pub
module) reused by endpoint (server-side) and call_client (client-side).
- remote_identity: None is load-bearing (not defaulted to placeholder).
- Integration tests updated to pin the self-signed server cert
fingerprint (the known-peer path).