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/views/CleanupView.vue

@@ -53,7 +53,8 @@ import TagMaintenanceCard from '../components/settings/TagMaintenanceCard.vue'
 </script>
 
 <style scoped>
-.fc-cleanup { max-width: 1100px; }
+/* width is capped + centered by SettingsView's .fc-settings container */
+.fc-cleanup { max-width: 100%; }
 .fc-section { margin-bottom: 28px; }
 .fc-section__title {
   font-size: 0.78rem;