Add Grafana Alloy support as alternative to deprecated Grafana Agent

Problem Grafana Agent reached End-of-Life on November 1, 2025 and no longer receives security or bug fixes. The current docker-compose.yml relies on Grafana Agent internally, leaving users on an unmaintained collector. Solution Add docker-compose.alloy.yml as an opt-in alternative setup using [Grafana Alloy]( the official open-source successor to Grafana Agent. The new setup uses three separate official images instead of a single bundled custom image: | Service | Image | |---------|-------| | Metrics collector | grafana/alloy:v1.16.1 | | Storage | prom/prometheus:v3.11.3 | | Visualization | grafana/grafana:13.0.1 | Pipeline Alloy scrapes the Supabase Metrics API every 60s over HTTPS, then pushes metrics to Prometheus via remote write. Grafana reads from Prometheus for visualization. Changes • docker-compose.alloy.yml — new compose file • alloy/config.alloy — Alloy pipeline configuration • grafana/datasource.alloy.yml — Grafan…