Add a native iOS client for relay-based file sharing

The SwiftUI app bundles the Go swarm engine through gomobile, so an iPhone is a real peer using the existing PAKE handshake, chunk verification, and relay fallback. XcodeGen builds the project and devicectl installs it on the paired phone.

apps/ios/Share/ShareApp.swift

@@ -0,0 +1,23 @@
+import SwiftUI
+
+@main
+struct ShareApp: App {
+  @StateObject private var model: AppModel
+
+  init() {
+    let model = AppModel()
+    _model = StateObject(wrappedValue: model)
+    Task { @MainActor in
+      SelfTest.runIfRequested(model: model)
+    }
+  }
+
+  var body: some Scene {
+    WindowGroup {
+      RootView()
+        .environmentObject(model)
+        .preferredColorScheme(.dark)
+        .tint(Theme.mint)
+    }
+  }
+}