Fix ERPNext and Forgejo probes

- ERPNext: custom blackbox module with Host: performancewest.net header
  (ERPNext multitenancy requires site name in Host for routing)
- Forgejo: add extra_hosts to blackbox-exporter so it can resolve
  host.docker.internal to reach forgejo on port 3000
- Blackbox http_erpnext module: sets Host header, expects 200

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -386,6 +386,8 @@ services:
     image: prom/blackbox-exporter:latest
     volumes:
       - ./monitoring/blackbox.yml:/etc/blackbox_exporter/config.yml:ro
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
     restart: unless-stopped
 
 volumes: