Add standalone backup script and admin update-check banner

ops/backup.sh snapshots Redis (BGSAVE, dynamic RDB path lookup) and
./config for standalone deployments, with retention. A background
service polls GitHub releases every 24h and surfaces an admin-only
banner in the UI when a newer version is published.

nodejs/app.js

@@ -34,6 +34,7 @@ app.contoller = require('./controller');
 require('./services/host_lookup');
 require('./services/host_scheduler');
 require('./services/dynamic_dns');
+require('./services/update_check');
 
 // Push pubsub over the socket and back.
 app.onListen.push(function(){