fix: remove promtail nested /var/log/traefik volume mount

Docker cannot mount to /var/log/traefik when /var/log is already
bind-mounted (read-only). The nested mount fails with 'read-only
file system' error in the overlay upper layer.

The mount was unused anyway — promtail config only reads syslog,
auth.log, and Docker container logs via the socket.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

roles/services/templates/docker-compose.yml.j2

@@ -526,7 +526,6 @@ services:
       - /var/log:/var/log:ro
       - /var/lib/docker/containers:/var/lib/docker/containers:ro
       - /var/run/docker.sock:/var/run/docker.sock:ro
-      - {{ services_root }}/traefik/logs:/var/log/traefik:ro
       - {{ services_root }}/loki/promtail.yml:/etc/promtail/config.yml:ro
     command: -config.file=/etc/promtail/config.yml