Remove pgdb1 host configuration and postgres service module.
The only consumer (Open WebUI on gunter) has migrated to local PostgreSQL.
Removed:
- hosts/pgdb1/ - host configuration
- services/postgres/ - service module (only used by pgdb1)
- postgres_rules from monitoring rules
- rebuild-all.sh (obsolete script)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>