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/Sources/VoiceCatCore/VoiceCatClient.swift

@@ -322,6 +322,20 @@ public final class VoiceCatClient {
         VoiceCatResult(vc_set_self_mute(handle, micMuted ? 1 : 0, deafened ? 1 : 0))
     }
 
+    // MARK: - AVAudioSession interruption hooks (iOS)
+
+    /// Pause miniaudio device I/O. Call when AVAudioSession interruption begins.
+    @discardableResult
+    public func audioSuspend() -> VoiceCatResult {
+        VoiceCatResult(vc_audio_suspend(handle))
+    }
+
+    /// Resume miniaudio device I/O. Call after re-activating AVAudioSession.
+    @discardableResult
+    public func audioResume() -> VoiceCatResult {
+        VoiceCatResult(vc_audio_resume(handle))
+    }
+
     // MARK: - Receive-side, per remote stream (LOCAL — no protocol traffic; docs/voice.md §10)
 
     @discardableResult