* Configure UFW firewall rules in common Ansible role
Add UFW configuration to the common role for Debian hosts:
- Default deny incoming, allow outgoing
- Allow all traffic on tailscale0 interface (mesh comms)
- Allow SSH port 22 as safety net
- Per-host allowed ports via ufw_allowed_ports variable
- Enable UFW after rules are applied
helsinki-a gets ports 80/443 for reverse proxy traffic.
Other Debian hosts only need Tailscale + SSH.
Closes PESO-79
* Remove unused alerting and rule_files from prometheus.yml
Alerting is handled by Grafana, not Prometheus Alertmanager.
The empty alertmanagers and rule_files sections were just noise.
Resolves PESO-74
