feat(call): wire CallClient TLS client-auth and server cert verifier selection (call/call-client-verifier-selection)

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).

crates/alknet-core/src/lib.rs

@@ -9,6 +9,7 @@
 pub mod auth;
 pub mod config;
 pub mod endpoint;
+pub mod fingerprint;
 pub mod store;
 pub mod types;