Migrate from iOS 17 Observation to iOS 16-compatible Combine architecture.

Lower deployment target to iOS 16, replace @Observable with ObservableObject, add navigation and UI compatibility shims, and include login smoke UI tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

suixinkan/App/suixinkanApp.swift

@@ -12,6 +12,10 @@ import SwiftUI
 struct suixinkanApp: App {
     @UIApplicationDelegateAdaptor(AppDelegate.self) private var appDelegate
 
+    init() {
+        AppUITestLaunchState.resetIfNeeded()
+    }
+
     var body: some Scene {
         WindowGroup {
             RootView()