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/DbMaintenanceCard.vue

@@ -1,7 +1,10 @@
 <template>
-  <v-card>
-    <v-card-title>Database maintenance</v-card-title>
-    <v-card-text>
+  <MaintenanceTile
+    icon="mdi-database-cog"
+    title="Database maintenance"
+    blurb="VACUUM ANALYZE + per-table bloat stats."
+    :open="busy"
+  >
       <p class="text-body-2 mb-3">
         VACUUM (ANALYZE) reclaims dead-tuple bloat — which slows the random
         showcase, since it samples physical blocks — and refreshes the query
@@ -42,8 +45,7 @@
       <p v-else class="text-caption mt-3" style="opacity: 0.6;">
         No table statistics yet.
       </p>
-    </v-card-text>
-  </v-card>
+  </MaintenanceTile>
 </template>
 
 <script setup>
@@ -51,6 +53,7 @@ import { onMounted, ref } from 'vue'
 
 import { toast } from '../../utils/toast.js'
 import { useDbMaintenanceStore } from '../../stores/dbMaintenance.js'
+import MaintenanceTile from '../common/MaintenanceTile.vue'
 import QueueStatusBar from './QueueStatusBar.vue'
 
 const store = useDbMaintenanceStore()