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>

monitoring/prometheus.yml

@@ -125,11 +125,11 @@ scrape_configs:
       - target_label: __address__
         replacement: blackbox-exporter:9115
 
-  # ── ERPNext CRM (login page returns 200) ───────────────────────────
+  # ── ERPNext CRM (requires Host header for site routing) ─────────────
   - job_name: pw_erpnext
     metrics_path: /probe
     params:
-      module: [http_internal]
+      module: [http_erpnext]
     static_configs:
       - targets:
           - http://erpnext:8000/api/method/ping