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/types.ts

@@ -0,0 +1,71 @@
+export type Severity = 'ok' | 'warn' | 'crit'
+
+export interface Release {
+  tag: string
+  url: string
+  publishedAt: string
+  prerelease: boolean
+  fromTag: boolean
+}
+
+export interface Repo {
+  fullName: string
+  url: string
+  releasesUrl: string
+  description: string
+  health: Severity
+  error: string
+  workflows: { total: number; failing: number; running: number }
+  prs: { open: number; waiting: number; failingChecks: number; oldestSeconds: number }
+  issues: { open: number; stale: number }
+  archived: boolean
+  up: boolean
+  refreshedAt: string
+  release: Release | null
+}
+
+export interface Alert {
+  repo: string
+  kind: string
+  severity: Severity
+  subject: string
+  detail: string
+  url: string
+  since: string
+}
+
+export interface Thresholds {
+  prWarnSeconds: number
+  prCritSeconds: number
+  issueStaleSeconds: number
+  workflowStuckSeconds: number
+  workflowDormantSeconds: number
+}
+
+export interface TrackerState {
+  now: string
+  lastRefresh: string
+  intervalSeconds: number
+  loaded: boolean
+  refreshing: boolean
+  manualRefresh: boolean
+  counts: { crit: number; warn: number }
+  thresholds: Thresholds
+  repos: Repo[]
+  alerts: Alert[]
+}
+
+/** One line in a repo block: every alert that targets the same URL, merged. */
+export interface Row {
+  kind: string
+  subject: string
+  detail: string
+  url: string
+  since: string
+  severity: Exclude<Severity, 'ok'>
+}
+
+export interface Block {
+  repo: Repo
+  rows: Row[]
+}