Fix webinar registration redirecting to ladl.link/undefined.

Exempt public register POST from cross-site CSRF, collect email on the
landing form, and handle API errors instead of navigating to a missing
success_url.

Co-authored-by: Cursor <cursoragent@cursor.com>

bootstrap/app.php

@@ -13,6 +13,11 @@ return Application::configure(basePath: dirname(__DIR__))
         health: '/up',
     )
     ->withMiddleware(function (Middleware $middleware): void {
+        // Public event registration is posted from ladl.link (cross-site); session CSRF cannot bind there.
+        $middleware->validateCsrfTokens(except: [
+            'q/*/register',
+        ]);
+
         $middleware->redirectGuestsTo(fn (Request $request) => route('sso.connect', [
             'redirect' => $request->fullUrl(),
         ]));