feat(settings): tidy Maintenance tab into compact tiles + center the views (pass 2)

Goal (operator 2026-06-18): the overview of a Settings tab fits one unscrolled
viewport; expanding a tile to read into it is the only reason to scroll.

- Every Maintenance card converted to the collapsible MaintenanceTile (collapsed
  by default = icon + short title + one-line blurb). Task cards (ML backfill,
  centroids, thumbnails, archive re-extract, missing-file repair, DB maintenance)
  sit in a responsive grid; running tasks auto-expand. Tagging config (suggestion
  thresholds, allowlist, aliases) grouped in one Tagging section as collapsible
  tiles; Backup is its own collapsible tile.
- Three labeled sections mirror the Cleanup tab: Backfills and reprocessing /
  Tagging / Storage.
- Center the whole Settings surface: SettingsView is now a centered, width-capped
  (1140px) column so the tab strip and every panel sit in a tidy centered measure
  (was full-width). CleanupView drops its own left-aligned max-width to fill it.

All card logic unchanged - only the chrome.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/settings/BackupCard.vue

@@ -1,7 +1,9 @@
 <template>
-  <v-card class="fc-backup-card">
-    <CardHeading icon="mdi-database-export" title="Backups" />
-    <v-card-text>
+  <MaintenanceTile
+    icon="mdi-database-export"
+    title="Backups"
+    blurb="Database + image backups, schedules and restore."
+  >
       <p class="fc-muted text-body-2 mb-4">
         pg_dump for the database (fast, nightly-schedulable);
         tar+zstd for the images (slow, manual only). Files live in
@@ -80,8 +82,6 @@
         @delete="onDelete"
         @tag="onTag"
       />
-    </v-card-text>
-
     <BackupConfirmModal
       v-model="confirmOpen"
       :action="confirmAction"
@@ -90,7 +90,7 @@
       :description="confirmDescription"
       @confirm="onConfirmSubmit"
     />
-  </v-card>
+  </MaintenanceTile>
 </template>
 
 <script setup>
@@ -98,7 +98,7 @@ import { computed, onMounted, onUnmounted, ref } from 'vue'
 
 import { useBackupStore } from '../../stores/backup.js'
 import BackupConfirmModal from '../modal/DestructiveConfirmModal.vue'
-import CardHeading from '../common/CardHeading.vue'
+import MaintenanceTile from '../common/MaintenanceTile.vue'
 import BackupRunsTable from './BackupRunsTable.vue'
 
 const store = useBackupStore()