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/PerUserTuningView.swift

@@ -0,0 +1,71 @@
+import SwiftUI
+import VoiceCatCore
+
+struct PerUserTuningView: View {
+    let user: User
+    @Bindable var session: SessionState
+    @Environment(\.dismiss) private var dismiss
+
+    @State private var gain: Float = 1.0
+    @State private var muted = false
+    @State private var noiseReduction = false
+
+    private var streamsForUser: [StreamSummary] {
+        session.client.listUserStreams(user.id)
+    }
+
+    var body: some View {
+        NavigationStack {
+            Form {
+                Section("Volume") {
+                    HStack {
+                        Text("Gain")
+                        Slider(value: $gain, in: 0...2, step: 0.05) { _ in
+                            applyToAllStreams()
+                        }
+                        .accessibilityLabel("Volume gain for \(user.nickname)")
+                        Text(String(format: "%.0f%%", gain * 100))
+                            .monospacedDigit()
+                            .frame(width: 44, alignment: .trailing)
+                    }
+                    Toggle("Mute", isOn: $muted)
+                        .onChange(of: muted) { _, _ in applyToAllStreams() }
+                        .accessibilityLabel("Mute \(user.nickname)")
+                }
+
+                Section("Audio Processing") {
+                    Toggle("Noise Reduction", isOn: $noiseReduction)
+                        .onChange(of: noiseReduction) { _, _ in applyToAllStreams() }
+                        .accessibilityLabel("Noise reduction for \(user.nickname)")
+                }
+            }
+            .navigationTitle(user.nickname)
+            .navigationBarTitleDisplayMode(.inline)
+            .toolbar {
+                ToolbarItem(placement: .confirmationAction) {
+                    Button("Done") { dismiss() }
+                }
+            }
+        }
+        .onAppear {
+            // Load from first stream if available
+            let streams = streamsForUser
+            if let first = streams.first {
+                let (_, state) = session.client.getRemoteStream(userId: user.id, streamId: first.id)
+                if let s = state {
+                    gain = s.gain
+                    muted = s.muted
+                    noiseReduction = s.noiseReduction
+                }
+            }
+        }
+    }
+
+    private func applyToAllStreams() {
+        for stream in streamsForUser {
+            session.client.setRemoteStream(
+                userId: user.id, streamId: stream.id,
+                gain: gain, muted: muted, noiseReduction: noiseReduction)
+        }
+    }
+}