feat(crypto,cli,transport): daily protocol-mask rotation at 05:00 MSK

Both server and client deterministically rotate the on-wire obfuscation mask
(SNI, HTTP Host/User-Agent/Server headers, UDP padding profile) at 05:00 Moscow
time (02:00 UTC) every day, derived from the CA fingerprint + UTC date — no
network coordination needed.

- aura-crypto::masks: MaskSet + 4 palettes (16 SNI, 10 UA, 5 Server, 4 padding
  profiles); derive_mask_for_msk_date via HKDF-SHA256(salt="aura-mask-v1-salt",
  ikm=ca_fp||"YYYY-MM-DD", info="aura-mask-v1"); ca_fingerprint with built-in
  base64 PEM decode (no new deps).
- aura-cli::masks: MaskRotator (Arc<RwLock<MaskSet>>) + Hinnant's civil_from_days
  for manual UTC date math; scheduler picks next 02:00 UTC strictly (avoids
  busy-loop at boundary); spawned at startup in server::run/client::run.
- aura-transport: PADDING_PROFILES + next_bucket_for_profile (profile 0 byte-for-
  byte equals legacy pad_to_https_size); TcpOpts gains user_agent/server_header;
  UdpOpts gains padding_profile; MultiServer holds Arc<UdpServer>/Arc<TcpServer>
  with set_udp_opts/set_tcp_opts so rotation propagates without restart.
- Backward-compatible: defaults preserve previous behavior; existing 97 tests
  unchanged. 17 new tests (derive determinism + date variation, civil-from-days
  known points incl. 1970-01-01/2000-02-29/2024->2025, next-rotation boundary,
  msk_today offset, profile equivalence, base64 round-trip, full mask-driven
  UDP loopback). Total: 114 passed, clippy/fmt clean. No new workspace deps.

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

crates/aura-transport/tests/tcp_loopback.rs

@@ -71,6 +71,7 @@ async fn tcp_loopback_end_to_end_masquerade() {
     run_case(TcpOpts {
         masquerade: true,
         host: "cdn.example.com".to_string(),
+        ..TcpOpts::default()
     })
     .await;
 }