feat(dashboards): scheduler health strip, failing-source rollup, 24h activity sparkline, credential staleness nudge

D1 scheduler visibility: AppSetting last-tick stamp on every Beat tick +
GET /api/sources/schedule-status (last_tick_at/next_due_at/due_now/auto_sources)
+ SchedulerStatusBar on the Subscriptions tab (re-polled every 30s).

D2 failing-source rollup: ?failing=true on the sources list + FailingSourcesCard
on Downloads with per-source and bulk "retry" (re-runs the feed via /check).

D3 activity sparkline: GET /api/downloads/activity hourly buckets + CSS bar
chart by the stat chips (failures stacked in error color); refreshes on live poll.

D4 credential staleness: surface last_verified age + "re-verify recommended"
warning past 30d; also fixes the dead last_verified_at field-name mismatch so
the verification row renders at all.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/subscriptions/DownloadsTab.vue

@@ -12,6 +12,12 @@
           live
         </span>
         <v-spacer />
+        <DownloadActivitySparkline
+          v-if="store.activity.buckets.length"
+          :buckets="store.activity.buckets"
+          :hours="store.activity.hours"
+          class="fc-dl__spark"
+        />
         <v-btn variant="text" icon @click="refresh">
           <v-icon>mdi-refresh</v-icon>
           <v-tooltip activator="parent" location="top">Refresh</v-tooltip>
@@ -41,6 +47,14 @@
       {{ String(store.error) }}
     </v-alert>
 
+    <FailingSourcesCard
+      :sources="store.failing"
+      :retrying-ids="sourcesStore.checkingIds"
+      :retrying-all="retryingAll"
+      @retry="onRetrySource"
+      @retry-all="onRetryAll"
+    />
+
     <div v-if="store.loading && store.events.length === 0" class="fc-dl__loading">
       <v-progress-circular indeterminate color="accent" size="36" />
     </div>
@@ -103,15 +117,20 @@ import { computed, onMounted, onUnmounted, reactive, ref, watch } from 'vue'
 import { useRoute } from 'vue-router'
 
 import { useDownloadsStore } from '../../stores/downloads.js'
+import { useSourcesStore } from '../../stores/sources.js'
 import DownloadEventRow from '../downloads/DownloadEventRow.vue'
 import DownloadDetailModal from '../downloads/DownloadDetailModal.vue'
 import DownloadStatChips from './DownloadStatChips.vue'
+import DownloadActivitySparkline from './DownloadActivitySparkline.vue'
+import FailingSourcesCard from './FailingSourcesCard.vue'
 import MaintenanceMenu from './MaintenanceMenu.vue'
 import DownloadsFilterPopover from './DownloadsFilterPopover.vue'
 
 const route = useRoute()
 const store = useDownloadsStore()
+const sourcesStore = useSourcesStore()
 const filterModel = ref({ ...store.filter })
+const retryingAll = ref(false)
 
 // Free-text search (client-side over the loaded events) + a toggle to
 // hide "no-change" scheduled scans (status=ok/skipped with 0 files) so
@@ -138,9 +157,51 @@ async function refresh() {
   await Promise.all([
     store.loadFirst(),
     store.loadStats(24),
+    store.loadActivity(24),
+    store.loadFailing(),
   ])
 }
 
+// Retry a single failing source (re-runs its whole feed) then refresh the
+// rollup + stats so the operator sees it move.
+async function onRetrySource(source) {
+  try {
+    await sourcesStore.checkNow(source.id)
+    globalThis.window?.__fcToast?.({ text: `Retry queued for ${source.artist_name || source.platform}`, type: 'success' })
+  } catch (e) {
+    if (e?.body?.download_event_id) {
+      globalThis.window?.__fcToast?.({ text: 'Already running — see below', type: 'info' })
+    } else {
+      globalThis.window?.__fcToast?.({ text: `Retry failed: ${e?.detail || e?.message || e}`, type: 'error' })
+    }
+  } finally {
+    await Promise.all([store.loadFailing(), store.loadStats(24), store.loadFirst()])
+  }
+}
+
+async function onRetryAll(sources) {
+  retryingAll.value = true
+  let ok = 0
+  let conflict = 0
+  try {
+    for (const s of sources) {
+      try {
+        await sourcesStore.checkNow(s.id)
+        ok += 1
+      } catch (e) {
+        if (e?.body?.download_event_id) conflict += 1
+      }
+    }
+  } finally {
+    retryingAll.value = false
+    await Promise.all([store.loadFailing(), store.loadStats(24), store.loadFirst()])
+  }
+  const parts = []
+  if (ok) parts.push(`${ok} queued`)
+  if (conflict) parts.push(`${conflict} already running`)
+  globalThis.window?.__fcToast?.({ text: parts.join(', ') || 'Nothing to retry', type: 'info' })
+}
+
 // Live auto-refresh: while any download is queued or running, poll the
 // stats + first page every 4s so the operator can watch events succeed/
 // fail in real time without hitting Refresh. Polling stops automatically
@@ -156,10 +217,10 @@ function startPolling() {
   if (pollId) return
   pollId = setInterval(async () => {
     if (document.hidden) return
-    // Refresh stats cheaply every tick; only reload the event list when
-    // there's active work to reflect (keeps idle ticks light).
-    await store.loadStats(24)
-    if (liveActive.value) await store.loadFirst()
+    // Refresh stats + sparkline cheaply every tick; only reload the event
+    // list + failing rollup when there's active work (keeps idle ticks light).
+    await Promise.all([store.loadStats(24), store.loadActivity(24)])
+    if (liveActive.value) await Promise.all([store.loadFirst(), store.loadFailing()])
   }, POLL_MS)
 }
 function stopPolling() {
@@ -288,6 +349,7 @@ async function openDetail(id) {
   display: flex; gap: 12px; align-items: center; flex-wrap: wrap;
 }
 .fc-dl__nochange { flex: 0 0 auto; }
+.fc-dl__spark { flex: 0 0 auto; margin-right: 4px; max-width: 240px; }
 .fc-dl__live {
   display: inline-flex; align-items: center; gap: 5px;
   font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.06em;