feat(proto,pki,cli): in-band CRL push (closes last v2 limitation)

Server now pushes its signed CRL to each connecting client right after the
handshake; the client verifies the signature against the CA and applies the
revocation list to its verifier (and caches it on disk for restarts).
Removes the v1 "CRL distributed out-of-band" honest limitation.

Wire (multiplexed over existing PacketConnection, no trait change):
control envelope = MAGIC[4]=[0xAA,0xAA,0xC0,0x01] || kind(u8) || u32_be(len)
  || payload. IPv4/IPv6 start with 0x4X/0x6X, so 0xAA cannot collide; an old
peer just drops it as a junk packet in the TUN — back-compat preserved.

- aura-proto: ControlKind { CrlPush, CrlAck, Unknown }, encode/decode_control_
  envelope, CONTROL_ENVELOPE_MAGIC; 7 frame tests.
- aura-pki: CrlStore::{encode_signed, save_signed, decode_signed_verified,
  load_signed_verified} — ECDSA-P256/SHA-256 from the CA private key against
  a textual "CRL-Aura-v1" body + --SIGNATURE--; 7 signing tests. ring 0.17
  added crate-local (already in lockfile via rustls-webpki).
- aura-cli: crl_push module — server pushes via conn.send_packet on accept;
  client wraps the Arc<dyn PacketConnection> in AcceptPushedCrlConn which
  sniffs the magic in recv_packet, verifies the signature, updates the
  AuraCertVerifier, caches to disk. PkiSection gets ca_key, crl_push (default
  true), accept_pushed_crl (default true).
- 5 in_band_crl integration tests via mock PacketConnection.

Workspace: 235 tests passed (+28), clippy -D warnings clean, fmt clean. v2
COMPLETE — all 9 honest v1 limitations resolved (except sing-box, per user).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/aura-cli/src/lib.rs

@@ -16,6 +16,7 @@ pub mod admin;
 pub mod bench;
 pub mod client;
 pub mod config;
+pub mod crl_push;
 pub mod dial_targets;
 pub mod init;
 pub mod masks;