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/templates/crawler-alert.env.j2

@@ -6,3 +6,5 @@ CRAWLER_THRESHOLD={{ crawler_threshold }}
 CRAWLER_MAIL_CONTAINER=forgejo
 CRAWLER_MAIL_INI=/data/gitea/conf/app.ini
 CRAWLER_ROBOTS={{ crawler_robots_url }}
+CRAWLER_LIVE_LOG=/opt/traefik/logs/access.log
+CRAWLER_TEXTFILE={{ monitoring_textfile_dir }}/crawler.prom