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/components/AppHeader.vue

@@ -0,0 +1,59 @@
+<script setup lang="ts">
+import { faArrowsRotate, faSatelliteDish } from '@fortawesome/free-solid-svg-icons'
+import { FontAwesomeIcon } from '@fortawesome/vue-fontawesome'
+import { computed } from 'vue'
+import { Button } from '@/components/ui/button'
+import { ageLabel, ageSince, isZeroTime } from '@/lib/format'
+
+const props = defineProps<{
+  lastRefresh: string
+  nowMs: number
+  intervalSeconds: number
+  loaded: boolean
+  scanning: boolean
+  manualRefresh: boolean
+}>()
+defineEmits<{ rescan: [] }>()
+
+const updated = computed(() =>
+  props.loaded && !isZeroTime(props.lastRefresh) ? ageSince(props.lastRefresh, props.nowMs) : '',
+)
+const nextIn = computed(() => {
+  if (!updated.value) return ''
+  const left = Math.floor(
+    (Date.parse(props.lastRefresh) + props.intervalSeconds * 1000 - props.nowMs) / 1000,
+  )
+  return left > 0 ? ageLabel(left) : 'now'
+})
+</script>
+
+<template>
+  <header class="flex items-center justify-between gap-4">
+    <div class="flex items-center gap-3">
+      <span
+        class="border-border bg-surface text-link flex size-9 items-center justify-center rounded-md border"
+      >
+        <FontAwesomeIcon :icon="faSatelliteDish" aria-hidden="true" />
+      </span>
+      <span class="text-lg font-semibold tracking-tight">ghtracker</span>
+    </div>
+    <div class="text-muted-foreground flex items-center gap-5 text-sm">
+      <span v-if="updated" class="hidden sm:inline" data-test="updated">
+        Scanned {{ updated }} ago
+        <span class="text-muted-foreground/70"> · next in {{ nextIn }}</span>
+      </span>
+      <span v-else>Loading</span>
+      <Button
+        v-if="manualRefresh"
+        variant="outline"
+        size="sm"
+        :disabled="scanning"
+        data-test="rescan"
+        @click="$emit('rescan')"
+      >
+        <FontAwesomeIcon :icon="faArrowsRotate" :spin="scanning" aria-hidden="true" />
+        {{ scanning ? 'Rescanning…' : 'Rescan repositories' }}
+      </Button>
+    </div>
+  </header>
+</template>