monitoring: keep Loki chunks in S3, 90 days of logs and metrics

ops has 12 GB free on a 38 GB disk and the Traefik access log alone
is ~600 MB, so logs can't grow there. From 2026-11-14 Loki writes
chunks and index to Hetzner Object Storage (asxpio-loki-main, hel1)
with the existing project key, passed through loki.env and
-config.expand-env. Today's filesystem period ages out by retention.

Log retention goes from 14 to 90 days. Prometheus metrics are small
(~20 MB so far) and stay local, now for 90 days instead of 30.

Assisted-by: Claude:opus-5-5

ansible/roles/monitoring/tasks/main.yaml

@@ -30,6 +30,7 @@
       - { src: blackbox.yml.j2, dest: blackbox.yml }
       - { src: loki.yml.j2, dest: loki.yml }
       - { src: grafana.env.j2, dest: grafana.env, mode: "0600" }
+      - { src: loki.env.j2, dest: loki.env, mode: "0600" }
       - { src: datasources.yaml.j2, dest: grafana/provisioning/datasources/datasources.yaml }
       - { src: dashboards.yaml.j2, dest: grafana/provisioning/dashboards/dashboards.yaml }
       - { src: alerting.yaml.j2, dest: grafana/provisioning/alerting/alerting.yaml }