feat: add GitHub repository dashboard with Prometheus metrics

ghtracker authenticates as a GitHub App and scans a configured list of repositories on a schedule. It serves a dashboard, a JSON state endpoint, a health probe and Prometheus metrics.

The dashboard lists only items that need attention: failing workflows, pull requests that wait too long or fail their checks, stale issues and projects that failed to scan. It has search, dynamic filters and a button that rescans on demand. The Vue app is embedded in the Go binary.

The client protects the GitHub rate limit with conditional requests, a request reserve and Retry-After handling.

deploy/kubernetes/servicemonitor.yaml

@@ -0,0 +1,12 @@
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: ghtracker
+spec:
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: ghtracker
+  endpoints:
+    - port: http
+      path: /metrics
+      interval: 5m # series are computed from cached data; scraping faster adds nothing