docs(rust): add doc comments to delta enums and fix dead_code warnings (#24)

* docs(rust): add doc comments to delta enums and fix dead_code warnings

Add missing documentation to ProtocolDelta, CoreDelta, and BridgeDelta
enum variants and their struct fields across the protocol, core, and
bridge crates. Document the ChannelId::ROOT constant and the
take_delta_rx adapter method.

Fix dead_code warnings:
- keyring_disabled: add #[cfg] gate matching its callers
- snapshot_signature: add #[cfg(test)] for future test use

* fix(rust): correct `order` field docs to predecessor channel ID, narrow audio engine cfg gates

- Correct `order` field documentation in ProtocolDelta, SessionEvent,
  and BridgeEvent from 'sort order' to 'predecessor channel ID
  (TeamSpeak linked-list ordering hint)' per Copilot review feedback.
- Narrow AudioEngine voice_out_tx, voice_activity_selector, and mic_gain
  cfg gates from ios+macos+android to android-only, since these fields
  are only read from self in android_restart_voice_unit. On iOS/macOS the
  values are passed directly to the voice backend at construction time.

core/chanora_core/src/lib.rs

@@ -253,49 +253,87 @@ pub enum SessionEvent {
     },
     /// Audio route changed (speaker/earpiece/BT/wired headset).
     AudioRouteChanged {
+        /// New audio output route.
         route: AudioRoute,
     },
+    /// A client moved to a different channel.
     ClientMoved {
+        /// Unique client identifier.
         client_id: u64,
+        /// Destination channel.
         new_channel_id: u64,
     },
+    /// A new client connected.
     ClientJoined {
+        /// Unique client identifier.
         client_id: u64,
+        /// Channel the client joined.
         channel_id: u64,
+        /// Display nickname.
         name: String,
+        /// Microphone muted state.
         input_muted: bool,
+        /// Speaker muted state.
         output_muted: bool,
+        /// Whether this is a server query (bot) client.
         is_server_query: bool,
+        /// Client's talk power value.
         talk_power: i32,
+        /// Whether the server granted temporary talk power.
         talk_power_granted: bool,
     },
+    /// A client disconnected.
     ClientLeft {
+        /// Unique client identifier.
         client_id: u64,
+        /// Display nickname at time of disconnect.
         name: String,
     },
+    /// Client properties changed.
     ClientUpdated {
+        /// Unique client identifier.
         client_id: u64,
+        /// Microphone muted state.
         input_muted: bool,
+        /// Speaker muted state.
         output_muted: bool,
+        /// Whether this is a server query (bot) client.
         is_server_query: bool,
+        /// Client's talk power value.
         talk_power: i32,
+        /// Whether the server granted temporary talk power.
         talk_power_granted: bool,
     },
+    /// A new channel appeared.
     ChannelAdded {
+        /// Unique channel identifier.
         id: u64,
+        /// Parent channel ID.
         parent: u64,
+        /// Channel name.
         name: String,
+        /// Predecessor channel ID within the same parent (TeamSpeak
+        /// linked-list ordering hint). Zero means first child.
         order: i64,
+        /// Whether the channel requires a password.
         has_password: bool,
+        /// Talk power required to speak, or `None` when unrestricted.
         needed_talk_power: Option<i32>,
     },
+    /// A channel was deleted.
     ChannelRemoved {
+        /// Channel identifier.
         id: u64,
     },
+    /// Channel properties changed.
     ChannelUpdated {
+        /// Unique channel identifier.
         id: u64,
+        /// Channel name.
         name: String,
+        /// Whether the channel requires a password.
         has_password: bool,
+        /// Talk power required to speak, or `None` when unrestricted.
         needed_talk_power: Option<i32>,
     },
 }
@@ -2399,6 +2437,7 @@ async fn supervisor_loop(ctx: SupervisorContext) {
 /// the UI would render. Two snapshots with identical channel
 /// memberships, names, and orderings produce the same signature;
 /// any in-channel move, rename, or reorder produces a different one.
+#[cfg(test)]
 fn snapshot_signature(snap: &ServerSnapshot) -> u64 {
     use std::collections::hash_map::DefaultHasher;
     use std::hash::{Hash, Hasher};