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.

config.example.yaml

@@ -0,0 +1,23 @@
+listen: ':8080'
+refresh_interval: 6h # minimum 1m; each cycle costs roughly 6 + 2 per open PR requests per repo
+manual_refresh: true # the Refresh button and POST /refresh, limited to once per 5m; false disables them
+
+github:
+  app_id: 123456
+  private_key_file: /secrets/ghtracker.pem # or set $GHTRACKER_PRIVATE_KEY to the PEM contents
+  installation_id: 0 # 0 = discover per repo; needed when repos span several owners
+  api_url: https://api.github.com
+
+thresholds: # negative disables a check
+  pr_warn_after: 48h # non-draft PR open this long = warning
+  pr_crit_after: 168h # critical
+  issue_stale_after: 720h # no activity this long = warning (aggregated per repo)
+  workflow_stuck_after: 6h # queued / in progress this long = warning
+
+max_items: 100 # per repo, issues and PRs
+concurrency: 2
+
+repos:
+  - lukaszraczylo/kubemirror
+  - lukaszraczylo/semver-generator
+  - lukaszraczylo/traefikoidc