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/ActivityLogView.swift

@@ -0,0 +1,49 @@
+import SwiftUI
+
+struct ActivityLogView: View {
+    @Bindable var session: SessionState
+
+    private static let timeFormatter: DateFormatter = {
+        let fmt = DateFormatter()
+        fmt.dateStyle = .none
+        fmt.timeStyle = .medium
+        return fmt
+    }()
+
+    var body: some View {
+        ScrollViewReader { proxy in
+            List(session.activityLog) { entry in
+                HStack(alignment: .top, spacing: 8) {
+                    Text(Self.timeFormatter.string(from: entry.timestamp))
+                        .font(.caption2)
+                        .foregroundStyle(.secondary)
+                        .monospacedDigit()
+                        .frame(width: 64, alignment: .leading)
+                    Text(entry.text)
+                        .font(.caption)
+                }
+                .id(entry.id)
+                .listRowSeparator(.hidden)
+                .accessibilityElement(children: .combine)
+                .accessibilityLabel("\(Self.timeFormatter.string(from: entry.timestamp)): \(entry.text)")
+            }
+            .listStyle(.plain)
+            .onChange(of: session.activityLog.count) { _, _ in
+                if let last = session.activityLog.last {
+                    proxy.scrollTo(last.id, anchor: .bottom)
+                }
+            }
+        }
+        .navigationTitle("Activity")
+        .navigationBarTitleDisplayMode(.inline)
+        .overlay {
+            if session.activityLog.isEmpty {
+                ContentUnavailableView(
+                    "No Activity",
+                    systemImage: "bell.slash",
+                    description: Text("Events will appear here as they happen.")
+                )
+            }
+        }
+    }
+}