Add /donation/success route and flash messages for both outcomes

Cancelled donations now show "Donation failed, but thank you for
trying anyway." and successful ones show "Thank you for the
donation!" on the dashboard after redirect.

src/Website/Controller/HomeController.php

@@ -33,6 +33,16 @@ final class HomeController extends AbstractController
     #[Route(path: '/donation/cancel', name: 'website_donation_cancel')]
     public function donationCancel(): Response
     {
+        $this->addFlash('info', 'Donation failed, but thank you for trying anyway.');
+
+        return $this->redirectToRoute('game_dashboard');
+    }
+
+    #[Route(path: '/donation/success', name: 'website_donation_success')]
+    public function donationSuccess(): Response
+    {
+        $this->addFlash('success', 'Thank you for the donation!');
+
         return $this->redirectToRoute('game_dashboard');
     }
 }