feat(cli): automation bundle + identity-minimization features

Reduces manual setup steps and trims user-identifying data exposed by the
server/client, in the spirit of the deployment story: an operator on the
wire sees less, and the admin types fewer commands.

New CLI subcommands:
- `aura server-init`: one shot — pki init + issue-server + writes a ready
  server.toml with auto-detected egress iface; flags --enable-knock,
  --enable-cover-traffic, --no-nat, --run-as toggle the new transport
  defenses and privilege drop.
- `aura provision-client`: issues a client cert and assembles the full
  bundle (ca.crt + client.crt + client.key + client.toml in one directory)
  ready to hand over to the client device. --id is optional (defaults to
  a fresh UUIDv4, so client identities don't have to encode anything real).

Identity / log minimization:
- `aura pki issue-client --id` is now optional — UUIDv4 by default.
- `[server]/[client] no_logs = true` filters peer_id, client_ip,
  source_addr, client_id, local_ip, user, id, assigned_ip, peer field
  values through a custom tracing FormatFields layer (events still fire
  but the identifying fields are redacted before being written).
- `[client] bridges = [...]`: secondary server addresses; build_dial_targets
  shuffles them after the primary, so blocking one IP doesn't kill the
  client.
- Auto-detect egress iface in [server.nat] (via detect_default_egress_iface);
  egress_iface in config becomes optional with graceful fallback.

Config examples updated; backward-compatible (all new sections optional with
serde defaults). Workspace: 207 tests passed (+22), clippy -D warnings clean,
fmt clean. No new workspace deps.

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

crates/aura-cli/src/config.rs

@@ -114,6 +114,12 @@ pub struct ServerSection {
     /// server keeps its current credentials.
     #[serde(default)]
     pub run_as: Option<String>,
+    /// When `true`, the tracing layer suppresses event fields that would identify a peer
+    /// (`peer_id`, `client_ip`, `source_addr`, `client_id`, `local_ip`, `user`, `id`). The event
+    /// itself still fires (for operational counters like rx/tx packets), but no identifier is
+    /// written. Default `false` (verbose). See [`crate::no_logs`].
+    #[serde(default)]
+    pub no_logs: bool,
 }
 
 /// `[server.nat]` section: v2 auto-NAT configuration. See [`crate::nat`] for the apply / rollback
@@ -191,6 +197,17 @@ pub struct ClientSection {
     /// (or already non-root) the client keeps its current credentials. See [`crate::privdrop`].
     #[serde(default)]
     pub run_as: Option<String>,
+    /// When `true`, the tracing layer suppresses event fields that would identify the user
+    /// (`peer_id`, `client_ip`, `source_addr`, `client_id`, `local_ip`, `user`, `id`). Default
+    /// `false` (verbose). See [`crate::no_logs`].
+    #[serde(default)]
+    pub no_logs: bool,
+    /// Optional fallback server addresses tried in random order if the primary `server_addr`
+    /// fails on every transport. Each entry is an IP (or `IP:port`); the per-transport ports come
+    /// from `[transport]` as for the primary endpoint. Empty / omitted means no fallbacks.
+    /// See [`crate::dial_targets::build_dial_targets`].
+    #[serde(default)]
+    pub bridges: Vec<String>,
 }
 
 /// `[tunnel]` section of `client.toml`.
@@ -346,6 +363,13 @@ pub struct TransportSection {
     pub masquerade: bool,
     /// `[transport.masks]`: daily protocol-mask rotation knobs.
     pub masks: MasksSection,
+    /// `[transport.knock]`: UDP port-knocking (probe-resistance) toggle. When `enabled`, the UDP
+    /// transport demands a 16-byte HMAC prefix on every HS datagram derived from the shared
+    /// `knock_secret_source`. Default `enabled = false` for backwards compat.
+    pub knock: KnockSection,
+    /// `[transport.cover]`: idle-time cover-traffic injection on the UDP transport. Default
+    /// `enabled = false`.
+    pub cover: CoverSection,
 }
 
 impl Default for TransportSection {
@@ -358,6 +382,59 @@ impl Default for TransportSection {
             obfuscate: true,
             masquerade: true,
             masks: MasksSection::default(),
+            knock: KnockSection::default(),
+            cover: CoverSection::default(),
+        }
+    }
+}
+
+/// `[transport.knock]` section: UDP port-knocking (probe-resistance) toggle. When `enabled`, the
+/// UDP transport requires a 16-byte HMAC prefix on every HS datagram derived from the shared key.
+///
+/// `knock_secret_source` selects how the 32-byte key is computed:
+///
+/// * `"ca_fingerprint"` (default): `SHA-256(CA-cert-DER)`. Both peers can compute this
+///   independently from the CA they already trust — no wire coordination needed.
+#[derive(Debug, Clone, Deserialize)]
+#[serde(default)]
+pub struct KnockSection {
+    /// Master switch. `false` (the default) keeps backwards compat — no knock prefix is added or
+    /// validated.
+    pub enabled: bool,
+    /// Selector for the shared knock key. Default `"ca_fingerprint"`.
+    pub knock_secret_source: String,
+}
+
+impl Default for KnockSection {
+    fn default() -> Self {
+        Self {
+            enabled: false,
+            knock_secret_source: "ca_fingerprint".to_string(),
+        }
+    }
+}
+
+/// `[transport.cover]` section: idle-time cover-traffic injection on the UDP transport. When
+/// `enabled`, an established `UdpConnection` periodically injects encrypted `Ping`s if no user
+/// DATA was sent in the previous interval, blurring on-wire bursts.
+#[derive(Debug, Clone, Deserialize)]
+#[serde(default)]
+pub struct CoverSection {
+    /// Master switch. `false` (the default) disables cover traffic.
+    pub enabled: bool,
+    /// Mean interval, in milliseconds, between cover-traffic attempts. Default `500`.
+    pub mean_interval_ms: u64,
+    /// Uniform jitter fraction applied to `mean_interval_ms` (e.g. `0.5` gives ±50%). Clamped
+    /// into `[0.0, 1.0)` by the transport layer. Default `0.5`.
+    pub jitter: f32,
+}
+
+impl Default for CoverSection {
+    fn default() -> Self {
+        Self {
+            enabled: false,
+            mean_interval_ms: 500,
+            jitter: 0.5,
         }
     }
 }