fix: wait for Blazor interactivity before redirect button click

The Redirect_NavigatesToSessionPage test was timing out because it clicked
the button before Blazor's interactive circuit was ready. The old check
(WaitForSelectorState.Attached) only verified DOM presence, not interactivity.

Now waits for __doPostBack function (bootstrapped by WebFormsPageBase.
OnAfterRenderAsync) as a reliable signal that Blazor event handlers are
wired up  same pattern used in PostBackTests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: csharpfritz

samples/AfterBlazorServerSide.Tests/Migration/ResponseRedirectTests.cs

@@ -32,15 +32,16 @@ public async Task Redirect_NavigatesToSessionPage()
                 Timeout = 30000
             });
 
+            // Wait for Blazor interactive circuit — OnAfterRenderAsync bootstraps __doPostBack
+            await page.WaitForFunctionAsync("typeof window.__doPostBack === 'function'",
+                null, new PageWaitForFunctionOptions { Timeout = 10000 });
+
             var card = page.Locator("[data-audit-control='redirect-basic-demo']");
             var button = card.Locator("button:has-text('Response.Redirect')");
 
-            // Ensure Blazor interactive circuit is ready before clicking
-            await button.WaitForAsync(new LocatorWaitForOptions { State = WaitForSelectorState.Attached, Timeout = 10000 });
             await button.ClickAsync();
 
-            // forceLoad: true triggers full page navigation (HTTP + prerender + SignalR)
-            // which needs generous timeout in CI
+            // forceLoad: true triggers full page navigation
             await page.WaitForURLAsync("**/migration/session", new PageWaitForURLOptions
             {
                 WaitUntil = WaitUntilState.Load,