fix(ios): restrict authentication capabilities and validate bootstrap types

Require iOS 18.4 for explicit upload denial in the isolated authentication window. Add origin-bound generated download policy, app-switcher privacy, typed metadata regressions and original community icon assets. Seven portable tests and Swift formatting checks pass; Apple SDK validation remains external.

ios/Sources/AuthenticationView.swift

@@ -7,7 +7,7 @@ struct AuthenticationView: View {
     var body: some View {
         NavigationStack {
             IsolatedAuthentication(url: destination, model: model)
-                .navigationTitle("Isolated web sign-in")
+                .navigationTitle(model.authenticationHost)
                 .navigationBarTitleDisplayMode(.inline)
                 .toolbar { Button("Close") { model.authentication = nil } }
         }
@@ -33,15 +33,26 @@ struct IsolatedAuthentication: UIViewRepresentable {
     }
     func updateUIView(_ uiView: WKWebView, context: Context) {}
     static func dismantleUIView(_ uiView: WKWebView, coordinator: Coordinator) {
-        uiView.stopLoading(); uiView.navigationDelegate = nil; uiView.uiDelegate = nil
+        uiView.stopLoading()
+        uiView.navigationDelegate = nil
+        uiView.uiDelegate = nil
     }
     final class Coordinator: NSObject, WKNavigationDelegate, WKUIDelegate {
         let model: BrowserModel
         init(_ model: BrowserModel) { self.model = model }
-        func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction,
-                     decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
+        func webView(_ webView: WKWebView, didStartProvisionalNavigation navigation: WKNavigation!) {
+            model.authenticationHost = webView.url?.host ?? "Sign in"
+        }
+        func webView(
+            _ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction,
+            decisionHandler: @escaping (WKNavigationActionPolicy) -> Void
+        ) {
             guard let url = navigationAction.request.url, url.scheme == "https",
-                  url.user == nil, url.password == nil else { decisionHandler(.cancel); return }
+                url.user == nil, url.password == nil
+            else {
+                decisionHandler(.cancel)
+                return
+            }
             decisionHandler(.allow)
         }
         func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
@@ -50,8 +61,17 @@ struct IsolatedAuthentication: UIViewRepresentable {
                 model.web.load(URLRequest(url: url))
             }
         }
-        func webView(_ webView: WKWebView, requestMediaCapturePermissionFor origin: WKSecurityOrigin,
-                     initiatedByFrame frame: WKFrameInfo, type: WKMediaCaptureType,
-                     decisionHandler: @escaping (WKPermissionDecision) -> Void) { decisionHandler(.deny) }
+        func webView(
+            _ webView: WKWebView, requestMediaCapturePermissionFor origin: WKSecurityOrigin,
+            initiatedByFrame frame: WKFrameInfo, type: WKMediaCaptureType,
+            decisionHandler: @escaping (WKPermissionDecision) -> Void
+        ) { decisionHandler(.deny) }
+        func webView(
+            _ webView: WKWebView, runOpenPanelWith parameters: WKOpenPanelParameters,
+            initiatedByFrame frame: WKFrameInfo,
+            completionHandler: @escaping @MainActor @Sendable ([URL]?) -> Void
+        ) {
+            completionHandler(nil)
+        }
     }
 }