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

docs/operations/prometheus-alerts.yml

@@ -0,0 +1,55 @@
+groups:
+  - name: qpq-server
+    rules:
+      - alert: QpqServerDown
+        expr: up{job="qpq-server"} == 0
+        for: 1m
+        labels:
+          severity: critical
+        annotations:
+          summary: "qpq-server is down"
+          description: "Prometheus cannot scrape qpq-server metrics for > 1 minute."
+
+      - alert: QpqHighAuthFailureRate
+        expr: rate(auth_login_failure_total[5m]) > 10
+        for: 2m
+        labels:
+          severity: warning
+        annotations:
+          summary: "High authentication failure rate"
+          description: "{{ $value | printf \"%.1f\" }} auth failures/sec over 5 minutes."
+
+      - alert: QpqRateLimitActive
+        expr: rate(rate_limit_hit_total[5m]) > 5
+        for: 5m
+        labels:
+          severity: warning
+        annotations:
+          summary: "Rate limiting is actively rejecting requests"
+
+      - alert: QpqDeliveryQueueHigh
+        expr: delivery_queue_depth > 10000
+        for: 10m
+        labels:
+          severity: warning
+        annotations:
+          summary: "Delivery queue depth is high ({{ $value }})"
+
+      - alert: QpqDeliveryQueueCritical
+        expr: delivery_queue_depth > 100000
+        for: 5m
+        labels:
+          severity: critical
+        annotations:
+          summary: "Delivery queue depth is critical ({{ $value }})"
+
+      - alert: QpqLowAuthSuccessRatio
+        expr: >
+          rate(auth_login_success_total[5m])
+          / (rate(auth_login_success_total[5m]) + rate(auth_login_failure_total[5m]))
+          < 0.5
+        for: 10m
+        labels:
+          severity: warning
+        annotations:
+          summary: "Auth success ratio below 50%"