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/tasks/main.yaml

@@ -22,6 +22,8 @@
     - crawler-alert.timer
     - crawler-weekly.service
     - crawler-weekly.timer
+    - crawler-metrics.service
+    - crawler-metrics.timer
   notify: Reload systemd
 
 - name: Flush handlers
@@ -35,3 +37,4 @@
   loop:
     - crawler-alert.timer
     - crawler-weekly.timer
+    - crawler-metrics.timer