docs(operator): grant the usage breakdown tables to the DB user

[v0l]

#309 added a DELETE+INSERT rewrite of app_deployment_service_usage and app_deployment_volume_usage (lnvps_db/src/mysql.rs:4300-4331) without widening the documented operator grant, which was still SELECT everywhere plus UPDATE on app_deployment. In production the operator gets DELETE command denied and every deployment's breakdown stays empty; the totals still update, since those are an UPDATE on app_deployment.

Docs only — the grant itself is applied by hand on the database.

GRANT INSERT, DELETE ON lnvps.app_deployment_service_usage TO 'lnvps_operator'@'%';
GRANT INSERT, DELETE ON lnvps.app_deployment_volume_usage TO 'lnvps_operator'@'%';

From the lnvps channel.