feat(ia): wave 2 — Activity becomes the whole-app pulse; Overview gets the health strip

The Activity tab only knew Celery — the GPU agent (the majority of processing)
and the download pipeline were invisible there. Two new self-polling panels:

- GpuActivityPanel: queue depths + triage verdicts (defects / file-ok /
  unprobed, top reason buckets) with a jump to Maintenance -> Failed
  processing. The triage detail refetches only when the error count moves.
- DownloadsActivityPanel: 24h stat chips + failing-source names with a jump
  into Subscriptions.

Both panels join the Activity tab under Queues+workers AND double as the
Overview health strip (side-by-side grid under the Celery summary) — one
component set, so Overview answers 'is everything healthy?' across all
systems. SystemStatsCards reviewed: content still accurate, left as-is.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

frontend/src/views/SettingsView.vue

@@ -28,6 +28,13 @@
           class="mt-4"
           @open-activity="tab = 'activity'"
         />
+        <!-- Health strip (2026-07-02): the same GPU + downloads panels the
+             Activity tab uses — Overview answers "is everything healthy?"
+             across ALL systems, not just the Celery queues above. -->
+        <div class="fc-health-row mt-4">
+          <GpuActivityPanel @open-maintenance="tab = 'maintenance'" />
+          <DownloadsActivityPanel />
+        </div>
         <v-alert
           v-if="system.stats && (system.stats.tasks.pending + system.stats.tasks.queued) > 0"
           type="info" variant="tonal" class="mt-4" closable
@@ -38,7 +45,7 @@
       </v-window-item>
 
       <v-window-item value="activity">
-        <SystemActivityTab />
+        <SystemActivityTab @open-maintenance="tab = 'maintenance'" />
       </v-window-item>
 
       <v-window-item value="cleanup">
@@ -58,6 +65,8 @@ import { useSystemStore } from '../stores/system.js'
 import SystemStatsCards from '../components/settings/SystemStatsCards.vue'
 import SystemActivitySummary from '../components/settings/SystemActivitySummary.vue'
 import SystemActivityTab from '../components/settings/SystemActivityTab.vue'
+import GpuActivityPanel from '../components/settings/GpuActivityPanel.vue'
+import DownloadsActivityPanel from '../components/settings/DownloadsActivityPanel.vue'
 import MaintenancePanel from '../components/settings/MaintenancePanel.vue'
 import CleanupView from './CleanupView.vue'
 import { useMLStore } from '../stores/ml.js'
@@ -93,4 +102,13 @@ watch(tab, (t) => {
 .fc-settings {
   max-width: 1140px;
 }
+/* Overview health strip: the two pulse panels side by side, stacking on
+   narrow screens. Cancel the panels' own bottom margin — the row owns gaps. */
+.fc-health-row {
+  display: grid;
+  grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
+  gap: 16px;
+  align-items: start;
+}
+.fc-health-row :deep(.v-card) { margin-bottom: 0 !important; }
 </style>