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/ServerListStore.swift

@@ -0,0 +1,106 @@
+import Foundation
+import Security
+
+final class ServerListStore {
+    static let shared = ServerListStore()
+
+    private let groupId = "group.cat.voice.VoiceCat"
+    private let keychainService = "cat.voice.VoiceCatiOS"
+
+    // MARK: - App Group Container
+
+    var appGroupContainer: URL {
+        guard let url = FileManager.default.containerURL(
+            forSecurityApplicationGroupIdentifier: groupId)
+        else {
+            // Fall back to app-only support dir if App Groups are unavailable (e.g. simulator
+            // without entitlements). TOFU pins won't be shared with the broadcast extension,
+            // but connect + auth still work.
+            return FileManager.default.urls(for: .applicationSupportDirectory,
+                                            in: .userDomainMask).first!
+        }
+        return url
+    }
+
+    private var voicecatDir: URL {
+        let dir = appGroupContainer.appendingPathComponent("voicecat", isDirectory: true)
+        try? FileManager.default.createDirectory(at: dir,
+                                                  withIntermediateDirectories: true)
+        return dir
+    }
+
+    var tofuStorePath: String { voicecatDir.appendingPathComponent("tofu_pins.txt").path }
+
+    private var serversURL: URL { voicecatDir.appendingPathComponent("servers.json") }
+
+    // MARK: - Server list persistence
+
+    func load() -> [SavedServer] {
+        guard let data = try? Data(contentsOf: serversURL),
+              let list = try? JSONDecoder().decode([SavedServer].self, from: data)
+        else { return [] }
+        return list
+    }
+
+    func save(_ servers: [SavedServer]) {
+        guard let data = try? JSONEncoder().encode(servers) else { return }
+        try? data.write(to: serversURL, options: .atomic)
+    }
+
+    // MARK: - Keychain
+
+    func savePassword(_ password: String, tag: String) {
+        let data = Data(password.utf8)
+        let query: [CFString: Any] = [
+            kSecClass: kSecClassGenericPassword,
+            kSecAttrService: keychainService,
+            kSecAttrAccount: tag,
+            kSecAttrAccessGroup: groupId,
+        ]
+        SecItemDelete(query as CFDictionary)
+        var add = query
+        add[kSecValueData] = data
+        SecItemAdd(add as CFDictionary, nil)
+    }
+
+    func loadPassword(tag: String) -> String? {
+        let query: [CFString: Any] = [
+            kSecClass: kSecClassGenericPassword,
+            kSecAttrService: keychainService,
+            kSecAttrAccount: tag,
+            kSecAttrAccessGroup: groupId,
+            kSecReturnData: true,
+            kSecMatchLimit: kSecMatchLimitOne,
+        ]
+        var result: AnyObject?
+        guard SecItemCopyMatching(query as CFDictionary, &result) == errSecSuccess,
+              let data = result as? Data
+        else { return nil }
+        return String(data: data, encoding: .utf8)
+    }
+
+    func deletePassword(tag: String) {
+        let query: [CFString: Any] = [
+            kSecClass: kSecClassGenericPassword,
+            kSecAttrService: keychainService,
+            kSecAttrAccount: tag,
+            kSecAttrAccessGroup: groupId,
+        ]
+        SecItemDelete(query as CFDictionary)
+    }
+
+    // MARK: - Broadcast credentials (shared with ReplayKit extension)
+
+    func writeBroadcastCredentials(server: SavedServer, nickname: String?) {
+        let creds = BroadcastCredentials(
+            host: server.host,
+            port: Int(server.port),
+            authMode: server.authMode.rawValue,
+            username: server.authMode == .password ? server.savedUsername : (nickname ?? ""),
+            tofuPinsPath: tofuStorePath
+        )
+        guard let data = try? JSONEncoder().encode(creds) else { return }
+        let url = voicecatDir.appendingPathComponent("broadcast_credentials.json")
+        try? data.write(to: url, options: .atomic)
+    }
+}