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/SavedServer.swift

@@ -0,0 +1,24 @@
+import Foundation
+
+struct SavedServer: Codable, Identifiable, Equatable {
+    let id: UUID
+    var host: String
+    var port: UInt16
+    var authMode: AuthMode
+    var savedUsername: String
+    var keychainTag: String
+
+    enum AuthMode: String, Codable { case guest, password }
+
+    init(id: UUID = UUID(), host: String, port: UInt16,
+         authMode: AuthMode = .guest, savedUsername: String = "", keychainTag: String = "") {
+        self.id = id
+        self.host = host
+        self.port = port
+        self.authMode = authMode
+        self.savedUsername = savedUsername
+        self.keychainTag = keychainTag.isEmpty ? id.uuidString : keychainTag
+    }
+
+    var displayString: String { "\(host):\(port)" }
+}