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.

CMakePresets.json

@@ -90,15 +90,19 @@
     },
     {
       "name": "apple-ios",
-      "displayName": "Apple iOS device (XCFramework slice, scaffolding)",
-      "description": "SCAFFOLDING — not yet CI-validated; build on macOS to verify. Cross-compiles a static libvoicecat.a for iOS device (arm64-ios). One slice of the XCFramework. Server/tools/tests off. Requires VCPKG_ROOT and a macOS host with iOS SDK.",
+      "displayName": "Apple iOS device (XCFramework slice)",
+      "description": "Cross-compiles a static libvoicecat.a for iOS device (arm64). One slice of the XCFramework. Server/tools/tests off. Requires VCPKG_ROOT and a macOS host with iOS SDK. Uses cmake/vcpkg-overlays/triplets/arm64-ios.cmake (release-only, correct autoconf host triple).",
       "inherits": "vcpkg-common",
       "binaryDir": "${sourceDir}/build/apple-ios",
       "cacheVariables": {
         "CMAKE_BUILD_TYPE": "Release",
         "CMAKE_SYSTEM_NAME": "iOS",
         "CMAKE_SYSTEM_PROCESSOR": "arm64",
+        "CMAKE_OSX_ARCHITECTURES": "arm64",
+        "CMAKE_OSX_SYSROOT": "iphoneos",
+        "CMAKE_OSX_DEPLOYMENT_TARGET": "17.0",
         "VCPKG_TARGET_TRIPLET": "arm64-ios",
+        "VCPKG_OVERLAY_TRIPLETS": "${sourceDir}/cmake/vcpkg-overlays/triplets",
         "VOICECAT_BUILD_SERVER": "OFF",
         "VOICECAT_BUILD_TOOLS": "OFF",
         "VOICECAT_BUILD_TESTS": "OFF"
@@ -106,15 +110,19 @@
     },
     {
       "name": "apple-ios-sim",
-      "displayName": "Apple iOS simulator (XCFramework slice, scaffolding)",
-      "description": "SCAFFOLDING — not yet CI-validated; build on macOS to verify. Cross-compiles a static libvoicecat.a for iOS simulator (arm64-ios-sim on Apple Silicon). One slice of the XCFramework. Server/tools/tests off. Requires VCPKG_ROOT and a macOS host with iOS simulator SDK.",
+      "displayName": "Apple iOS simulator (XCFramework slice)",
+      "description": "Cross-compiles a static libvoicecat.a for iOS simulator (arm64-ios-simulator). One slice of the XCFramework. Server/tools/tests off. Requires VCPKG_ROOT and a macOS host with iOS simulator SDK. Uses cmake/vcpkg-overlays/triplets/arm64-ios-simulator.cmake (release-only, correct autoconf host triple).",
       "inherits": "vcpkg-common",
       "binaryDir": "${sourceDir}/build/apple-ios-sim",
       "cacheVariables": {
         "CMAKE_BUILD_TYPE": "Release",
         "CMAKE_SYSTEM_NAME": "iOS",
         "CMAKE_SYSTEM_PROCESSOR": "arm64",
-        "VCPKG_TARGET_TRIPLET": "arm64-ios-sim",
+        "CMAKE_OSX_ARCHITECTURES": "arm64",
+        "CMAKE_OSX_SYSROOT": "iphonesimulator",
+        "CMAKE_OSX_DEPLOYMENT_TARGET": "17.0",
+        "VCPKG_TARGET_TRIPLET": "arm64-ios-simulator",
+        "VCPKG_OVERLAY_TRIPLETS": "${sourceDir}/cmake/vcpkg-overlays/triplets",
         "VOICECAT_BUILD_SERVER": "OFF",
         "VOICECAT_BUILD_TOOLS": "OFF",
         "VOICECAT_BUILD_TESTS": "OFF"