feat(ios): implement SwiftUI companion with isolated WKWebView sessions

Add HTTPS onboarding, origin policy, native recovery/settings, isolated web sign-in and file export. Portable production URL policy tests pass on Linux; all Swift sources parse. Xcode build and simulator validation remain required on macOS.

ios/Sources/YuvomiApp.swift

@@ -0,0 +1,8 @@
+import SwiftUI
+
+@main
+struct YuvomiApp: App {
+    var body: some Scene {
+        WindowGroup { ContentView() }
+    }
+}