crawler_alert, monitoring: AI crawler metrics and dashboards

crawler-alert.py --metrics (5-minute timer) reads what the Traefik
access log gained since the last run, judges every request that names
an AI bot exactly like the weekly report (vendor IP ranges, forward-
confirmed rDNS, Meta's ASN) and writes cumulative counters to the
node_exporter textfile directory. Verdicts are cached per bot and IP
for a week, so DNS only sees new addresses; range files are refetched
once a day. It covers every router, while the mails keep watching
Forgejo only.

New dashboard "AI crawlers", and a row of it on the overview.

The overview's load gauge divided node_load1 by a count with fewer
labels, which matches nothing; aggregate both sides by host.

Assisted-by: Claude:opus-5-5

ansible/roles/crawler_alert/files/crawler-metrics.service

@@ -0,0 +1,12 @@
+[Unit]
+Description=Crawler counters for Prometheus (node_exporter textfile)
+After=docker.service
+
+[Service]
+Type=oneshot
+EnvironmentFile=/etc/crawler-alert.env
+# Every router, not only Forgejo's; fewer DNS lookups per 5-minute run
+Environment=CRAWLER_METRICS_ROUTER= CRAWLER_RDNS_MAX=100
+ExecStart=/usr/local/bin/crawler-alert.py --metrics
+Nice=10
+TimeoutStartSec=4min