feat(ios): audio overhaul, Join/Leave Voice, channel-id sync fix, stereo mic capture

Three iOS client problems fixed plus a new core stereo-mic capture ABI:

1. Channel-id sync bug (mic button permanently dimmed): SessionState never
   synced currentChannelId from the self user's channelId on connect, so the
   mic button (gated on currentChannelId == 0) stayed dimmed. Added
   syncSelfChannel() (mirrors macOS MainWindowController.swift:461,491,522);
   called from init/.channelList/.userJoined/.userLeft/.userUpdated/.joinResult.
   Added applyServerMuteState() + serverMuted/serverDeafened to VoiceState.

2. Join/Leave Voice button: replaced icon-only mic toggle with explicit
   text button (parity with macOS). Mute/deafen disable when not in voice.

3. IOSAudioRouter.swift (new): full AVAudioSession routing layer — input
   port selection, built-in mic orientation/polar patterns, Bluetooth
   HFP/A2DP/Off modes, Standard/Raw mic processing, stereo capture, AirPlay,
   UserDefaults persistence. AudioSessionManager delegates to it.

4. Core stereo-mic capture (append-only ABI): vc_set_capture_channels()
   lets the core open the mic device in stereo (2-ch interleaved). LocalStream
   gains capture_channels; ensure_audio_running reads it; audio_engine.cpp
   capture_accum_ + on_capture updated to channel-aware accumulation. Test
   test_stereo_mic_capture (headless, L!=R stereo round-trip). Swift wrapper
   VoiceCatClient.setCaptureChannels.

5. Settings UI rework: AVAudioSession-derived input/output tree replaces
   miniaudio device picker.

6. iOS deployment target raised to 18.0 (Package.swift + project.pbxproj).
   swift-tools-version 6.0 with swiftLanguageModes .v5.

Docs: tech-stack.md, architecture.md, voice.md, roadmap.md, building.md
updated; stale 'vc_audio_suspend/resume deferred' claims corrected.

Verified: ctest --preset dev 21/21 green; swift test 6/6 green;
xcodebuild -target VoiceCatiOS -sdk iphonesimulator BUILD SUCCEEDED.

clients/apple/iOS/VoiceCatiOS/SessionState.swift

@@ -22,6 +22,8 @@ struct VoiceState {
     var micActive = false
     var selfMuted = false
     var selfDeafened = false
+    var serverMuted = false
+    var serverDeafened = false
     var inputMode: VoiceCatInputMode = .voiceActivation
     var vadThreshold: Float = 0.025
     var level: Float = 0.0
@@ -54,6 +56,7 @@ final class SessionState {
         AudioSessionManager.shared.client = client
         refreshChannels()
         refreshUsers()
+        syncSelfChannel()
         refreshDevices()
         client.onEvent = { [weak self] ev in
             Task { @MainActor [weak self] in self?.handleEvent(ev) }
@@ -75,8 +78,16 @@ final class SessionState {
         switch ev.type {
         case .channelList:
             refreshChannels()
-        case .userJoined, .userLeft, .userUpdated:
+            syncSelfChannel()
+        case .userJoined, .userLeft:
             refreshUsers()
+            syncSelfChannel()
+        case .userUpdated:
+            refreshUsers()
+            syncSelfChannel()
+            if let me = users.first(where: { $0.id == selfUserId }) {
+                applyServerMuteState(muted: me.serverMuted, deafened: me.serverDeafened)
+            }
         case .textMessage:
             let sender = users.first(where: { $0.id == ev.userId })?.nickname ?? "Unknown"
             messages.append(ChatMessage(
@@ -118,6 +129,29 @@ final class SessionState {
         if activityLog.count > 500 { activityLog.removeFirst() }
     }
 
+    // MARK: - Self-channel / server-mute sync
+
+    /// Sync currentChannelId from the self user's channelId in the user list. Mirrors macOS
+    /// MainWindowController.swift:461,491,522. The server auto-places every authed user into
+    /// the Lobby (channel 1) on connect, but without this sync currentChannelId stays 0 and
+    /// the mic button (gated on currentChannelId == 0) stays permanently dimmed.
+    private func syncSelfChannel() {
+        if let me = users.first(where: { $0.id == selfUserId }) {
+            currentChannelId = me.channelId
+        }
+    }
+
+    /// Apply server-side mute/deafen state — mirrors macOS MainWindowController.swift:693-700.
+    /// iOS was previously ignoring server mute/deafen entirely.
+    private func applyServerMuteState(muted: Bool, deafened: Bool) {
+        if muted && !voiceState.serverMuted { addActivity("You have been server-muted") }
+        if deafened && !voiceState.serverDeafened { addActivity("You have been server-deafened") }
+        if !muted && voiceState.serverMuted { addActivity("Server mute cleared") }
+        if !deafened && voiceState.serverDeafened { addActivity("Server deafen cleared") }
+        voiceState.serverMuted = muted
+        voiceState.serverDeafened = deafened
+    }
+
     // MARK: - Data refresh
 
     func refreshChannels() { channels = client.listChannels() }
@@ -160,6 +194,13 @@ final class SessionState {
         if result == .ok {
             voiceState.micActive = true
             voiceState.localStreamId = streamId
+            // Apply the user's capture channel selection (mono/stereo) from IOSAudioRouter.
+            // The core opens the capture device via miniaudio on the next engine start;
+            // vc_set_capture_channels tells it to open in stereo (2) or mono (1).
+            let channels = IOSAudioRouter.shared.captureChannels.channelCount
+            if channels != 1 {
+                client.setCaptureChannels(streamId: streamId, channels: channels)
+            }
         } else {
             addActivity("Failed to start mic: \(result.description)")
         }