feat(thumb-backfill): MaintenancePanel — wire ThumbnailBackfillCard into grid, broaden intro to cover non-ML backfills

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

frontend/src/components/settings/MaintenancePanel.vue

@@ -1,13 +1,15 @@
 <template>
   <div class="fc-maint">
     <p class="text-body-2 mb-4">
-      Machine-assisted tagging controls. Backfill and centroid recompute run
-      nightly automatically; the allowlist auto-applies accepted tags to new
-      and existing images.
+      Operational backfills and tagging controls. The ML backfill and centroid
+      recompute run nightly automatically; the allowlist auto-applies accepted
+      tags to new and existing images. Use the cards below to trigger a
+      one-off pass.
     </p>
     <div class="fc-maint__grid">
       <MLBackfillCard />
       <CentroidRecomputeCard />
+      <ThumbnailBackfillCard />
     </div>
     <MLThresholdSliders class="mt-4" />
     <AllowlistTable class="mt-4" />
@@ -23,6 +25,7 @@
 <script setup>
 import MLBackfillCard from './MLBackfillCard.vue'
 import CentroidRecomputeCard from './CentroidRecomputeCard.vue'
+import ThumbnailBackfillCard from './ThumbnailBackfillCard.vue'
 import MLThresholdSliders from './MLThresholdSliders.vue'
 import AllowlistTable from './AllowlistTable.vue'
 import AliasTable from './AliasTable.vue'