monitoring: add alerts for homelab-deploy build failures

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

services/monitoring/rules.yml

@@ -395,3 +395,21 @@ groups:
         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."
+  - name: homelab_deploy_rules
+    rules:
+      - alert: homelab_deploy_build_failed
+        expr: increase(homelab_deploy_build_host_total{status="failure"}[1h]) > 0
+        for: 0m
+        labels:
+          severity: warning
+        annotations:
+          summary: "Build failed for {{ $labels.host }} in repo {{ $labels.repo }}"
+          description: "Host {{ $labels.host }} failed to build from {{ $labels.repo }} repository."
+      - alert: homelab_deploy_builder_down
+        expr: up{job="homelab-deploy-builder"} == 0
+        for: 5m
+        labels:
+          severity: warning
+        annotations:
+          summary: "Homelab deploy builder not responding on {{ $labels.instance }}"
+          description: "Cannot scrape homelab-deploy-builder metrics from {{ $labels.instance }} for 5 minutes."