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.

crates/chanora_protocol/src/adapter.rs

@@ -471,6 +471,9 @@ impl ProtocolClient {
         }
     }
 
+    /// Takes ownership of the delta receiver channel. Returns `None` if already
+    /// taken. Must be called exactly once during initialization to subscribe to
+    /// incremental state changes.
     pub fn take_delta_rx(&self) -> Option<mpsc::Receiver<ProtocolDelta>> {
         self.delta_rx.lock().ok().and_then(|mut g| g.take())
     }

crates/chanora_protocol/src/dto.rs

@@ -168,52 +168,93 @@ pub struct ServerSnapshot {
 }
 
 impl ChannelId {
+    /// Root/top-level channel identifier.
     pub const ROOT: ChannelId = ChannelId(0);
 }
 
+/// Incremental state change emitted by the protocol adapter when the server tree changes.
+///
+/// Covers client joins, leaves, moves, and channel additions, removals, and updates.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub enum ProtocolDelta {
+    /// A client moved to a different channel.
     ClientMoved {
+        /// Unique client identifier.
         client_id: u64,
+        /// Destination channel identifier.
         new_channel_id: u64,
     },
+    /// A new client appeared on the server.
     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 the client is a server query 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.
         name: String,
     },
+    /// A client's properties changed.
     ClientUpdated {
+        /// Unique client identifier.
         client_id: u64,
+        /// Microphone muted state.
         input_muted: bool,
+        /// Speaker muted state.
         output_muted: bool,
+        /// Whether the client is a server query 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 {
+        /// Channel identifier.
         id: u64,
+        /// Parent channel identifier.
         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 has a password.
         has_password: bool,
+        /// Needed talk power, or `None` when unrestricted.
         needed_talk_power: Option<i32>,
     },
+    /// A channel was deleted.
     ChannelRemoved {
+        /// Channel identifier.
         id: u64,
     },
+    /// Channel properties changed.
     ChannelUpdated {
+        /// Channel identifier.
         id: u64,
+        /// Channel name.
         name: String,
+        /// Whether the channel has a password.
         has_password: bool,
+        /// Needed talk power, or `None` when unrestricted.
         needed_talk_power: Option<i32>,
     },
 }