feat(ios): ship iOS SwiftUI client (VoiceCatiOS)

Full SwiftUI app at clients/apple/iOS/VoiceCatiOS.xcodeproj:
- 24 Swift source files: AppState + SessionState (@Observable @MainActor),
  AudioSessionManager (AVAudioSession owner + interruption/route handling),
  ServerListStore/SavedServer (App Group container + Keychain sharing),
  and 14 SwiftUI views covering the full feature set
- NavigationSplitView on iPad, TabView on iPhone (horizontalSizeClass)
- Channel tree via OutlineGroup, user list with context menu admin actions
- PTT via DragGesture(minimumDistance: 0) + @GestureState
- onEvent closures hop to MainActor via Task { @MainActor in ... }
- App Group: group.cat.voice.VoiceCat (shared with future ReplayKit extension)

C ABI: add vc_audio_suspend / vc_audio_resume (AudioEngine::suspend/resume)
called by AudioSessionManager on AVAudioSession interruption events.

XCFramework: add ios-arm64 and ios-arm64-simulator slices to build-xcframework.sh;
Package.swift gains .iOS(.v17) platform; CMakePresets.json adds apple-ios /
apple-ios-sim presets with arm64-ios / arm64-ios-simulator vcpkg triplets.

Verified: xcodebuild -target VoiceCatiOS -sdk iphonesimulator26.5 BUILD SUCCEEDED.

clients/apple/iOS/VoiceCatiOS/Views/SettingsView.swift

@@ -0,0 +1,94 @@
+import SwiftUI
+import VoiceCatCore
+
+struct SettingsView: View {
+    @Environment(AppState.self) private var appState
+    @Bindable var session: SessionState
+
+    var body: some View {
+        NavigationStack {
+            Form {
+                // Voice input section
+                Section("Voice Input") {
+                    Picker("Input Mode", selection: Binding(
+                        get: { session.voiceState.inputMode },
+                        set: { session.setInputMode($0) }
+                    )) {
+                        Text("Voice Activation").tag(VoiceCatInputMode.voiceActivation)
+                        Text("Push to Talk").tag(VoiceCatInputMode.pushToTalk)
+                        Text("Always On").tag(VoiceCatInputMode.alwaysOn)
+                    }
+                    .accessibilityLabel("Voice input mode")
+
+                    if session.voiceState.inputMode == .voiceActivation {
+                        VStack(alignment: .leading, spacing: 4) {
+                            Text("VAD Threshold: \(String(format: "%.3f", session.voiceState.vadThreshold))")
+                                .font(.caption)
+                            Slider(
+                                value: Binding(
+                                    get: { Double(session.voiceState.vadThreshold) },
+                                    set: { session.setVadThreshold(Float($0)) }
+                                ),
+                                in: 0.001...0.1, step: 0.001
+                            )
+                            .accessibilityLabel("Voice activation threshold")
+                        }
+                    }
+                }
+
+                // Audio device section
+                if !session.devices.isEmpty {
+                    Section("Input Device") {
+                        Picker("Microphone", selection: Binding(
+                            get: { session.voiceState.currentDeviceId ?? "" },
+                            set: { id in
+                                session.voiceState.currentDeviceId = id.isEmpty ? nil : id
+                                if session.voiceState.localStreamId != 0 {
+                                    session.client.setInputDevice(
+                                        streamId: session.voiceState.localStreamId,
+                                        deviceId: id.isEmpty ? nil : id)
+                                }
+                            }
+                        )) {
+                            Text("Default").tag("")
+                            ForEach(session.devices) { dev in
+                                Text(dev.name).tag(dev.id)
+                            }
+                        }
+                        .accessibilityLabel("Microphone selection")
+                    }
+                }
+
+                // Admin section
+                if session.permissions.canAdminAccounts || session.permissions.isAdmin {
+                    Section("Administration") {
+                        NavigationLink("Manage Accounts") {
+                            AccountsView(session: session)
+                        }
+                        .accessibilityLabel("Manage server accounts")
+                    }
+                }
+
+                // Server info
+                Section("Server") {
+                    Button(role: .destructive) {
+                        session.stopMicStream()
+                        appState.disconnect()
+                    } label: {
+                        Label("Disconnect", systemImage: "phone.down")
+                            .foregroundStyle(.red)
+                    }
+                    .accessibilityLabel("Disconnect from server")
+                }
+
+                Section("About") {
+                    Text(VoiceCatClient.versionString)
+                        .font(.caption)
+                        .foregroundStyle(.secondary)
+                        .accessibilityLabel("Version: \(VoiceCatClient.versionString)")
+                }
+            }
+            .navigationTitle("Settings")
+        }
+    }
+}