Fix A11y tests (#5104)

* replace NavigationStack with ElementNavigationStack to allow the content to be rendered without a NavigationStack in a11y tests

* fix a11y tests

* update xcodeproject

* swiftformat fix

* use iOS 26.1 for CI

* use a wrapper to solve the issue for a11y tests

* ElementNavigationStack only uses the trick in DEBUG mode, and added a swiftlint rule to prevent the usage of NavigationStack

ElementX/Sources/Screens/StartChatScreen/View/StartChatScreen.swift

@@ -168,7 +168,7 @@ struct StartChatScreen_Previews: PreviewProvider, TestablePreview {
     }()
     
     static var previews: some View {
-        NavigationStack {
+        ElementNavigationStack {
             StartChatScreen(context: viewModel.context)
         }
     }