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-cli/src/config.rs

@@ -216,6 +216,8 @@ pub struct TransportSection {
     pub obfuscate: bool,
     /// TCP transport: prepend a minimal HTTP/1.1 preamble so the open resembles plain HTTP.
     pub masquerade: bool,
+    /// `[transport.masks]`: daily protocol-mask rotation knobs.
+    pub masks: MasksSection,
 }
 
 impl Default for TransportSection {
@@ -227,10 +229,31 @@ impl Default for TransportSection {
             quic_port: 444,
             obfuscate: true,
             masquerade: true,
+            masks: MasksSection::default(),
         }
     }
 }
 
+/// `[transport.masks]` section: automatic daily rotation of the obfuscation surface (SNI, HTTP
+/// preamble headers, padding profile) at 05:00 MSK.
+///
+/// Both peers derive the current mask from `(CA fingerprint, MSK date)`; no wire coordination is
+/// needed. When disabled, the static values from `[client] sni` / `[transport] obfuscate` /
+/// `[mimicry] sni` are used as before (pre-rotation behaviour).
+#[derive(Debug, Clone, Deserialize)]
+#[serde(default)]
+pub struct MasksSection {
+    /// `true` (default): rotate the obfuscation surface daily at 05:00 MSK = 02:00 UTC. `false`:
+    /// use the static TOML values verbatim.
+    pub enabled: bool,
+}
+
+impl Default for MasksSection {
+    fn default() -> Self {
+        Self { enabled: true }
+    }
+}
+
 impl TransportSection {
     /// Parse `order` into [`TransportMode`]s, rejecting unknown names and duplicates.
     pub fn modes(&self) -> anyhow::Result<Vec<TransportMode>> {
@@ -475,6 +498,7 @@ impl ClientConfigFile {
             tcp: TcpOpts {
                 masquerade: self.transport.masquerade,
                 host: self.client.sni.clone(),
+                ..TcpOpts::default()
             },
             attempt_timeout: Duration::from_secs(8),
         })