Notifications phase 2: a /push-sw.js service worker shows a system notification
on push and, on click, focuses an open CRM tab (or opens one) and deep-links to
the thread. usePushNotifications registers the SW, requests permission, subscribes
with IIOS's VAPID key, and stores the subscription via the be-crm door. The topbar
bell becomes a real enable/disable control (hidden when push is unsupported/demo).
Dashboard listens for the SW's notif-click message + a ?thread= deep link.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
