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/ArchiveReextractCard.vue

@@ -1,9 +1,12 @@
 <template>
   <!-- #713: re-extract PostAttachments that are really archives but were filed
        opaquely before the magic-byte gate, and attach their images to the post. -->
-  <v-card>
-    <v-card-title>Re-extract archive attachments</v-card-title>
-    <v-card-text>
+  <MaintenanceTile
+    icon="mdi-folder-zip-outline"
+    title="Re-extract archives"
+    blurb="Extract images from zip attachments filed opaquely."
+    :open="busy"
+  >
       <p class="text-body-2 mb-3">
         Some posts attached an archive (zip) whose images weren't extracted
         because the downloaded file had no usable extension. This scans existing
@@ -15,8 +18,7 @@
       </v-btn>
       <span v-if="queued" class="ml-3 text-caption text-success">Queued ✓</span>
       <QueueStatusBar queue="maintenance" queue-label="Maintenance" />
-    </v-card-text>
-  </v-card>
+  </MaintenanceTile>
 </template>
 
 <script setup>
@@ -24,6 +26,7 @@ import { ref } from 'vue'
 
 import { useApi } from '../../composables/useApi.js'
 import { toast } from '../../utils/toast.js'
+import MaintenanceTile from '../common/MaintenanceTile.vue'
 import QueueStatusBar from './QueueStatusBar.vue'
 
 const api = useApi()