Add push notifications (FCM) to an Android v6 CometChat app — Firebase + Dashboard provider setup, the push dependency, token registration after login, token refresh, unregister on logout, manifest/service wiring, badge count and notification navigation. THIN + docs-first: fetches the notifications docs for exact payloads. Triggers: 'add push notifications android cometchat', 'fcm cometchat android', 'notifications not arriving android', 'badge count android'.
