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/MLBackfillCard.vue

@@ -1,7 +1,10 @@
 <template>
-  <v-card>
-    <v-card-title>ML backfill</v-card-title>
-    <v-card-text>
+  <MaintenanceTile
+    icon="mdi-refresh"
+    title="ML backfill"
+    blurb="Re-run tagging + embeddings on images missing them."
+    :open="busy"
+  >
       <p class="text-body-2 mb-3">
         Re-run Camie + SigLIP on images missing predictions or embeddings
         for the current model versions. Safe to re-run.
@@ -11,14 +14,14 @@
       </v-btn>
       <span v-if="done" class="ml-3 text-caption">Enqueued.</span>
       <QueueStatusBar queue="ml" queue-label="ML" />
-    </v-card-text>
-  </v-card>
+  </MaintenanceTile>
 </template>
 
 <script setup>
 import { toast } from '../../utils/toast.js'
 import { ref } from 'vue'
 import { useMLStore } from '../../stores/ml.js'
+import MaintenanceTile from '../common/MaintenanceTile.vue'
 import QueueStatusBar from './QueueStatusBar.vue'
 const store = useMLStore()
 const busy = ref(false)