monitoring: remove duplicate rules from blackbox.nix

The rules were already added to rules.yml but the blackbox.nix file
still had them, causing duplicate 'groups' key errors.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/monitoring/blackbox.nix

@@ -42,9 +42,9 @@ in
     '';
   };
 
-  # Add blackbox scrape config and alert rules to Prometheus
-  services.prometheus = {
-    scrapeConfigs = [
+  # Add blackbox scrape config to Prometheus
+  # Alert rules are in rules.yml (certificate_rules group)
+  services.prometheus.scrapeConfigs = [
     {
       job_name = "blackbox_tls";
       metrics_path = "/probe";
@@ -73,37 +73,4 @@ in
       ];
     }
   ];
-
-    rules = [
-      ''
-        groups:
-          - name: certificate_rules
-            rules:
-              - alert: tls_certificate_expiring_soon
-                expr: (probe_ssl_earliest_cert_expiry - time()) < 86400 * 7
-                for: 1h
-                labels:
-                  severity: warning
-                annotations:
-                  summary: "TLS certificate expiring soon on {{ $labels.instance }}"
-                  description: "The TLS certificate for {{ $labels.instance }} expires in less than 7 days."
-              - alert: tls_certificate_expiring_critical
-                expr: (probe_ssl_earliest_cert_expiry - time()) < 86400
-                for: 0m
-                labels:
-                  severity: critical
-                annotations:
-                  summary: "TLS certificate expiring within 24h on {{ $labels.instance }}"
-                  description: "The TLS certificate for {{ $labels.instance }} expires in less than 24 hours. Immediate action required."
-              - alert: tls_probe_failed
-                expr: probe_success{job="blackbox_tls"} == 0
-                for: 5m
-                labels:
-                  severity: warning
-                annotations:
-                  summary: "TLS probe failed for {{ $labels.instance }}"
-                  description: "Cannot connect to {{ $labels.instance }} to check TLS certificate. The service may be down or unreachable."
-      ''
-    ];
-  };
 }