feat: add automated backups and Prometheus/Grafana monitoring stack (Steps 17-18)

Backups: pg_dump scripts with daily/weekly rotation and Cloudflare R2 offsite sync.
Monitoring: Prometheus, Grafana, node-exporter, cAdvisor in docker-compose; /metrics
endpoint activated via prometheus_client.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.env.example

@@ -173,6 +173,14 @@ SENTRY_DSN=
 SENTRY_ENVIRONMENT=production
 SENTRY_TRACES_SAMPLE_RATE=0.1
 
+# =============================================================================
+# MONITORING
+# =============================================================================
+ENABLE_METRICS=true
+GRAFANA_URL=https://grafana.wizard.lu
+GRAFANA_ADMIN_USER=admin
+GRAFANA_ADMIN_PASSWORD=changeme
+
 # =============================================================================
 # CLOUDFLARE R2 STORAGE
 # =============================================================================
@@ -192,6 +200,9 @@ R2_BUCKET_NAME=orion-media
 # Example: https://media.yoursite.com
 R2_PUBLIC_URL=
 
+# Cloudflare R2 backup bucket (used by scripts/backup.sh --upload)
+R2_BACKUP_BUCKET=orion-backups
+
 # =============================================================================
 # CLOUDFLARE CDN / PROXY
 # =============================================================================