feat(downloads): front-and-center "active now" panel with live elapsed timers

New ActiveDownloadsPanel pinned at the top of the Downloads tab shows what's
running (pulsing dot + live mm:ss timer counting from started_at) and what's
queued, so the operator can see activity at a glance without the running
filter. Backed by store.loadActive() which fetches running + pending
independent of the feed filter; refreshed every 4s by the existing live poll.

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

frontend/src/components/subscriptions/DownloadsTab.vue

@@ -43,6 +43,8 @@
       </div>
     </div>
 
+    <ActiveDownloadsPanel />
+
     <v-alert v-if="store.error" type="error" variant="tonal" closable class="my-4">
       {{ String(store.error) }}
     </v-alert>
@@ -124,6 +126,7 @@ import DownloadDetailModal from '../downloads/DownloadDetailModal.vue'
 import DownloadStatChips from './DownloadStatChips.vue'
 import DownloadActivitySparkline from './DownloadActivitySparkline.vue'
 import FailingSourcesCard from './FailingSourcesCard.vue'
+import ActiveDownloadsPanel from './ActiveDownloadsPanel.vue'
 import MaintenanceMenu from './MaintenanceMenu.vue'
 import DownloadsFilterPopover from './DownloadsFilterPopover.vue'
 
@@ -160,6 +163,7 @@ async function refresh() {
     store.loadStats(24),
     store.loadActivity(24),
     store.loadFailing(),
+    store.loadActive(),
   ])
 }
 
@@ -218,9 +222,10 @@ function startPolling() {
   if (pollId) return
   pollId = setInterval(async () => {
     if (document.hidden) return
-    // 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)])
+    // Refresh stats + sparkline + active panel every tick (so new runs
+    // surface within 4s even from idle); only reload the full event list +
+    // failing rollup when there's active work (keeps idle ticks light).
+    await Promise.all([store.loadStats(24), store.loadActivity(24), store.loadActive()])
     if (liveActive.value) await Promise.all([store.loadFirst(), store.loadFailing()])
   }, POLL_MS)
 }