feat: monitoring exporters, alerting, rate limiting, backups, incident runbook

- Add 4 Prometheus exporters: nginx (9113), redis (9121), postgres (9187), node (9100)
- Create 8 alerting rules in monitoring/prometheus/alerts.yml
- Update prometheus.yml with all scrape targets + rule_files
- WS connection rate limiting: max 5/IP/60s (Redis INCR)
- Admin login rate limiting: max 5/IP/5min (Redis INCR)
- 3 backup scripts: daily to R2 (14d), weekly full (8w), verify with restore test
- docs/incident-runbook.md with 5-tier triage + escalation
- Update CD workflow: full prometheus config + alerts seeding

docker-compose.prod.yml

@@ -104,6 +104,56 @@ services:
       timeout: 5s
       retries: 5
 
+  nginx-exporter:
+    image: nginx/nginx-prometheus-exporter:latest
+    container_name: linearvoid-nginx-exporter
+    restart: unless-stopped
+    command:
+      - "-nginx.scrape-uri=http://nginx/nginx-status"
+    networks:
+      - linearvoid-net
+    depends_on:
+      - nginx
+
+  redis-exporter:
+    image: oliver006/redis_exporter:latest
+    container_name: linearvoid-redis-exporter
+    restart: unless-stopped
+    command:
+      - "-redis.addr=redis://redis:6379"
+    networks:
+      - linearvoid-net
+    depends_on:
+      - redis
+
+  postgres-exporter:
+    image: prometheuscommunity/postgres-exporter:latest
+    container_name: linearvoid-postgres-exporter
+    restart: unless-stopped
+    environment:
+      DATA_SOURCE_NAME: "postgresql://linearvoid:${POSTGRES_PASSWORD:-linearvoid}@db:5432/linearvoid?sslmode=disable"
+    networks:
+      - linearvoid-net
+    depends_on:
+      - db
+
+  node-exporter:
+    image: prom/node-exporter:latest
+    container_name: linearvoid-node-exporter
+    restart: unless-stopped
+    pid: host
+    volumes:
+      - /proc:/host/proc:ro
+      - /sys:/host/sys:ro
+      - /:/rootfs:ro
+    command:
+      - "--path.procfs=/host/proc"
+      - "--path.sysfs=/host/sys"
+      - "--path.rootfs=/rootfs"
+      - "--collector.filesystem.mount-points-exclude=^/(sys|proc|dev|host|etc)($$|/)"
+    networks:
+      - linearvoid-net
+
   prometheus:
     image: prom/prometheus:latest
     container_name: linearvoid-prometheus