PWA: install button, one icon badge for Signal, mail and tasks due, share target for files, manifest launch handler

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -14,6 +14,8 @@ Mobile-first; bottom tabs on phones, side rail on iPad and desktop (tuned for 12
     docker compose up -d --build     # http://localhost:8080
     # or: node server.js
 
+**Install extras**: Settings has an Install button where the browser offers one (Chrome, Edge, Android). The installed app's icon badge counts unread Signal chats, unread mail and tasks that are overdue or due today. On Android and desktop Chrome/Edge, NE Hub appears in the Share menu: share files to it, pick a Seafile folder, and they upload.
+
 Put it behind your reverse proxy with HTTPS (needed for "Add to Home Screen" and the service worker),
 e.g. hub.necloud.us. Settings: `SEAFILE_URL`, `ONLYOFFICE_URL` env vars in docker-compose.yml.