Fix notification click URL by using correct data property

The web push payload sends the URL in data.url but the service
worker was looking for data.path, resulting in undefined URLs.

Also fix WebPush::Notification test to use url instead of path

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test/lib/web_push/persistent_request_test.rb

@@ -12,7 +12,7 @@ class WebPush::PersistentRequestTest < ActiveSupport::TestCase
     notification = WebPush::Notification.new(
       title: "Test",
       body: "Test notification",
-      path: "/test",
+      url: "/test",
       badge: 0,
       endpoint: ENDPOINT,
       endpoint_ip: PUBLIC_TEST_IP,