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.

src/lib/kinds.ts

@@ -0,0 +1,27 @@
+import {
+  faClockRotateLeft,
+  faCodePullRequest,
+  faCircleDot,
+  faGears,
+  faPlugCircleXmark,
+  faTriangleExclamation,
+  type IconDefinition,
+} from '@fortawesome/free-solid-svg-icons'
+
+/** Maps a server alert kind to the icon and group used in the UI. */
+export const KIND_ICON: Record<string, IconDefinition> = {
+  workflow_failed: faGears,
+  workflow_stuck: faGears,
+  pr_waiting: faCodePullRequest,
+  pr_checks_failing: faCodePullRequest,
+  issues_stale: faCircleDot,
+  refresh_failed: faPlugCircleXmark,
+  data_stale: faClockRotateLeft,
+  partial_data: faTriangleExclamation,
+}
+
+export function iconFor(kind: string): IconDefinition {
+  return KIND_ICON[kind] ?? faTriangleExclamation
+}
+
+export const DATA_KINDS = ['refresh_failed', 'data_stale', 'partial_data']