docs: add operational runbook, Grafana dashboard, and production docker-compose

Add comprehensive operational documentation:
- docs/operations/backup-restore.md: SQLCipher, file backend, blob backup/restore
- docs/operations/key-rotation.md: auth token, TLS, federation, DB key, OPAQUE rotation
- docs/operations/incident-response.md: playbook for common incidents
- docs/operations/scaling-guide.md: resource sizing, scaling triggers, capacity planning
- docs/operations/monitoring.md: Prometheus metrics, alert rules, log monitoring
- docs/operations/dashboards/qpq-overview.json: Grafana dashboard template
- docs/operations/prometheus.yml + alerts: Prometheus scrape and alert config
- docs/operations/grafana-provisioning/: auto-provisioning for datasources and dashboards
- docker-compose.prod.yml: production stack (server + Prometheus + Grafana)
- .env.example: documented environment variable template

.env.example

@@ -0,0 +1,20 @@
+# quicproquo Production Environment Variables
+# Copy this file to .env and fill in the values.
+
+# Server auth token (required, >= 16 characters)
+QPQ_AUTH_TOKEN=
+
+# SQLCipher database encryption key (required for store_backend=sql)
+QPQ_DB_KEY=
+
+# Ports (defaults shown)
+QPQ_LISTEN_PORT=7000
+QPQ_WS_PORT=9000
+
+# Optional features
+QPQ_SEALED_SENDER=false
+QPQ_REDACT_LOGS=true
+QPQ_WS_LISTEN=
+
+# Grafana admin password
+GRAFANA_ADMIN_PASSWORD=changeme