Fix target=_blank links opening Safari — add WKUIDelegate

Without a UI delegate, WKWebView hands target="_blank" and window.open()
links to the system (Safari). createWebViewWith now loads them in the
existing webview instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Marks/Views/BrowserView.swift

@@ -28,7 +28,7 @@ enum ReadingProgress {
 // MARK: - BrowserState
 
 @Observable
-final class BrowserState: NSObject, WKNavigationDelegate {
+final class BrowserState: NSObject, WKNavigationDelegate, WKUIDelegate {
     let webView: WKWebView
     var isLoading = false
     var canGoBack = false
@@ -56,6 +56,7 @@ final class BrowserState: NSObject, WKNavigationDelegate {
         scrollHandler = handler
         webView.configuration.userContentController.add(handler, name: "scrollProgress")
         webView.navigationDelegate = self
+        webView.uiDelegate = self
         webView.load(URLRequest(url: url))
     }
 
@@ -94,6 +95,15 @@ final class BrowserState: NSObject, WKNavigationDelegate {
     func webView(_: WKWebView, didFail _: WKNavigation!, withError _: Error) { isLoading = false }
     func webView(_: WKWebView, didFailProvisionalNavigation _: WKNavigation!, withError _: Error) { isLoading = false }
 
+    // target="_blank" and window.open() — load in the same webview instead of opening Safari
+    func webView(_ webView: WKWebView, createWebViewWith configuration: WKWebViewConfiguration,
+                 for action: WKNavigationAction, windowFeatures: WKWindowFeatures) -> WKWebView? {
+        if let url = action.request.url {
+            webView.load(URLRequest(url: url))
+        }
+        return nil
+    }
+
     func enterReaderMode(completion: @escaping () -> Void) {
         webView.evaluateJavaScript(readerModeJS) { _, _ in
             DispatchQueue.main.async {