Building GBIM Observability From Correlation IDs to a Populated k6 Dashboard

Summary In this iteration, I improved the observability of GBIM on both the backend and frontend, based on the latest origin/staging branch. The focus is not just on installing monitoring tools. It is about ensuring that operational data relevant to the application's workflow actually appears in Prometheus, Grafana, Sentry, GA4, and the k6 dashboard. Key changes include gbm_* custom Prometheus metrics, structured logs with end-to-end correlation IDs, GA4 event analytics for user activity, Promet