refactor(observation): migrate SwiftUI state

apps/ios/Sources/Screen/ScreenController.swift

@@ -1,14 +1,16 @@
 import ClawdisKit
+import Observation
 import SwiftUI
 import WebKit
 
 @MainActor
-final class ScreenController: ObservableObject {
+@Observable
+final class ScreenController {
     let webView: WKWebView
 
-    @Published var mode: ClawdisScreenMode = .canvas
-    @Published var urlString: String = ""
-    @Published var errorText: String?
+    var mode: ClawdisScreenMode = .canvas
+    var urlString: String = ""
+    var errorText: String?
 
     init() {
         let config = WKWebViewConfiguration()

apps/ios/Sources/Screen/ScreenTab.swift

@@ -2,7 +2,7 @@ import ClawdisKit
 import SwiftUI
 
 struct ScreenTab: View {
-    @EnvironmentObject private var appModel: NodeAppModel
+    @Environment(NodeAppModel.self) private var appModel
 
     var body: some View {
         ZStack(alignment: .top) {

apps/ios/Sources/Screen/ScreenWebView.swift

@@ -3,7 +3,7 @@ import SwiftUI
 import WebKit
 
 struct ScreenWebView: UIViewRepresentable {
-    @ObservedObject var controller: ScreenController
+    var controller: ScreenController
 
     func makeUIView(context: Context) -> WKWebView {
         self.controller.webView