feat(infra): add deploy tracking with PostgreSQL, Pushgateway & Grafana dashboard

Instrument the CD pipeline to record per-deploy and per-service metrics
(build time, image size, startup time, health status) into PostgreSQL and
push gauges to Pushgateway. Adds a Grafana dashboard with 13 panels covering
deploy frequency, build performance, service health, and history.

New files:
- scripts/mac-mini/init-deploy-tracking.sql (idempotent DDL)
- scripts/deploy-metrics.sh (bash library for CI)
- docker/grafana/provisioning/datasources/deploy-tracking.yml
- docker/grafana/dashboards/deploy-tracking.json

Modified:
- docker/prometheus/prometheus.yml (pushgateway scrape job)
- .github/workflows/cd-macmini.yml (build/health instrumentation)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/prometheus/prometheus.yml

@@ -111,3 +111,11 @@ scrape_configs:
   #     - targets: ['nutriphi-backend:3037']
   #   metrics_path: '/metrics'
   #   scrape_interval: 30s
+
+  # ============================================
+  # Pushgateway (deploy metrics, batch jobs)
+  # ============================================
+  - job_name: 'pushgateway'
+    honor_labels: true
+    static_configs:
+      - targets: ['pushgateway:9091']