Qt: Fix URL bar lag during back/forward navigation

The URL bar was showing the previous URL instead of updating immediately
during back/forward navigation. This was caused by coreFrameUrl() returning
the current document URL instead of the target navigation URL.

Fix by checking if there's an active document loader with a different URL
and returning that target URL instead. This ensures the URL bar updates
synchronously with back/forward navigation.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: mnutt

Source/WebKitLegacy/qt/WebCoreSupport/QWebFrameAdapter.cpp

@@ -446,6 +446,13 @@ void QWebFrameAdapter::renderCompositedLayers(WebCore::GraphicsContext& context,
 // FIXME: this might not be necessary, but for the sake of not breaking things, we'll use that for now.
 QUrl QWebFrameAdapter::coreFrameUrl() const
 {
+    // For back/forward navigation, use the target URL if available
+    if (auto* activeLoader = frame->loader().activeDocumentLoader()) {
+        const URL& targetUrl = activeLoader->url();
+        if (!targetUrl.isEmpty() && targetUrl != frame->document()->url()) {
+            return targetUrl;
+        }
+    }
     return frame->document()->url();
 }