feat(docker): add healthchecks for celery-beat and node-exporter

celery-beat: check that the schedule file was modified within the last
120 seconds (confirms beat is ticking).
node-exporter: check /metrics endpoint for build_info metric.

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

docker-compose.yml

@@ -97,7 +97,7 @@ services:
     restart: always
     profiles:
       - full  # Only start with: docker compose --profile full up -d
-    command: celery -A app.core.celery_config beat --loglevel=info
+    command: celery -A app.core.celery_config beat --loglevel=info --schedule=/tmp/celerybeat-schedule
     env_file: .env
     environment:
       DATABASE_URL: postgresql://orion_user:secure_password@db:5432/orion_db
@@ -109,7 +109,11 @@ services:
         condition: service_healthy
     mem_limit: 256m
     healthcheck:
-      disable: true
+      test: ["CMD-SHELL", "test $(( $(date +%s) - $(stat -c %Y /tmp/celerybeat-schedule 2>/dev/null || echo 0) )) -lt 120 || exit 1"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 30s
     networks:
       - backend
 
@@ -207,6 +211,11 @@ services:
       - "--path.rootfs=/rootfs"
       - "--collector.filesystem.mount-points-exclude=^/(sys|proc|dev|host|etc)($$|/)"
     mem_limit: 64m
+    healthcheck:
+      test: ["CMD-SHELL", "wget -qO- http://localhost:9100/metrics | grep -q 'node_exporter_build_info' || exit 1"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
     networks:
       - monitoring