monitoring: scrape cadvisor/nodeexporter/telegraf at /metrics not /

prometheus-scrape.metrics_path was '/' which made prometheus-docker-sd scrape
the HTML root and fail with 'INVALID is not a valid start token', leaving the
targets up=0. Fixes per-container (cadvisor) + host (node_exporter) metrics so
they can be wired into the DRPC insights MCP for per-node resource attribution.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nodeexporter.yml

@@ -18,6 +18,7 @@ services:
       - "prometheus-scrape.enabled=true"
       - "prometheus-scrape.port=9100"
       - "prometheus-scrape.job_name=nodeexporter"
+      - "prometheus-scrape.metrics_path=/metrics"
       - "org.label-schema.group=monitoring"
     networks:
       - monitoring