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/ChatView.swift

@@ -0,0 +1,94 @@
+import SwiftUI
+import VoiceCatCore
+
+struct ChatView: View {
+    @Bindable var session: SessionState
+    @State private var composeText = ""
+    @State private var scope: VoiceCatTextScope = .channel
+    @State private var privateTargetId: UInt32 = 0
+
+    var body: some View {
+        VStack(spacing: 0) {
+            // Message list
+            ScrollViewReader { proxy in
+                ScrollView {
+                    LazyVStack(alignment: .leading, spacing: 8) {
+                        ForEach(session.messages) { msg in
+                            ChatBubble(message: msg)
+                                .id(msg.id)
+                        }
+                    }
+                    .padding()
+                }
+                .onChange(of: session.messages.count) { _, _ in
+                    if let last = session.messages.last {
+                        proxy.scrollTo(last.id, anchor: .bottom)
+                    }
+                }
+            }
+
+            Divider()
+
+            // Compose bar
+            HStack(spacing: 8) {
+                TextField("Message…", text: $composeText, axis: .vertical)
+                    .lineLimit(1...5)
+                    .textFieldStyle(.roundedBorder)
+                    .accessibilityLabel("Message text field")
+                    .onSubmit { sendMessage() }
+
+                Button {
+                    sendMessage()
+                } label: {
+                    Image(systemName: "arrow.up.circle.fill")
+                        .imageScale(.large)
+                }
+                .disabled(composeText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
+                          || session.currentChannelId == 0)
+                .accessibilityLabel("Send message")
+            }
+            .padding(.horizontal)
+            .padding(.vertical, 8)
+        }
+        .navigationTitle("Chat")
+        .navigationBarTitleDisplayMode(.inline)
+    }
+
+    private func sendMessage() {
+        let text = composeText.trimmingCharacters(in: .whitespacesAndNewlines)
+        guard !text.isEmpty else { return }
+        session.sendText(text, scope: .channel)
+        composeText = ""
+    }
+}
+
+private struct ChatBubble: View {
+    let message: ChatMessage
+
+    private var timeString: String {
+        let fmt = DateFormatter()
+        fmt.dateStyle = .none
+        fmt.timeStyle = .short
+        return fmt.string(from: message.timestamp)
+    }
+
+    var body: some View {
+        VStack(alignment: .leading, spacing: 2) {
+            HStack(spacing: 4) {
+                Text(message.senderName)
+                    .font(.caption)
+                    .fontWeight(.semibold)
+                    .foregroundStyle(.secondary)
+                Text(timeString)
+                    .font(.caption2)
+                    .foregroundStyle(.tertiary)
+            }
+            Text(message.text)
+                .font(.body)
+                .textSelection(.enabled)
+        }
+        .frame(maxWidth: .infinity, alignment: .leading)
+        .accessibilityElement(children: .combine)
+        .accessibilityLabel("\(message.senderName) at \(timeString): \(message.text)")
+    }
+}