feat(settings): tidy Cleanup tab into sectioned compact tiles (pass 1)

The Cleanup + Maintenance sections had ~17 full-width stacked cards with long
descriptions — a hunt to scan. Operator wants compact, sectioned, scannable tiles
(2026-06-18: keep both tabs, group inside, compact tiles in a grid).

New common/MaintenanceTile.vue: a compact expandable tile (icon + short title +
one-line blurb collapsed; click the header to expand the full controls/preview/
result inline; keyboard-accessible button + focus ring;  tints the
icon,  keeps a running task expanded).

Cleanup tab (this pass) restructured into 3 sections — Import-filter audits
(Min dimensions, Transparency, Single-color) / Duplicates & posts (Bare posts,
Duplicate posts, Deduplicate videos, Gated-post previews) / Tags (Unused, Legacy,
Reset content tagging, Standardize casing) — each a responsive grid of tiles.
PostMaintenanceCard split into 2 tiles, TagMaintenanceCard into 4. Moved
VideoDedupCard + GatedPurgeCard from the Maintenance tab here (both are
destructive content cleanup). All card logic unchanged — only the chrome.

Maintenance tab tiling is pass 2 (TODO noted in MaintenancePanel).

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

frontend/src/components/settings/MaintenancePanel.vue

@@ -17,9 +17,11 @@
     <DbMaintenanceCard class="mt-6" />
     <ArchiveReextractCard class="mt-6" />
     <MissingFileRepairCard class="mt-6" />
-    <VideoDedupCard class="mt-6" />
-    <GatedPurgeCard class="mt-6" />
     <BackupCard class="mt-6" />
+    <!-- VideoDedupCard + GatedPurgeCard moved to the Cleanup tab (2026-06-18):
+         both are destructive content cleanup, so "remove unwanted stuff" now
+         lives in one place. -->
+    <!-- TODO(2026-06-18): tile-ify this tab's cards into sections too (pass 2). -->
     <!-- TagMaintenanceCard moved to Cleanup tab (v26.05.25.7) — it
          operates on the existing library which fits the Cleanup-tab
          theme, and clusters with the other audit cards. LegacyMigrationCard
@@ -39,8 +41,6 @@ import AliasTable from './AliasTable.vue'
 import DbMaintenanceCard from './DbMaintenanceCard.vue'
 import ArchiveReextractCard from './ArchiveReextractCard.vue'
 import MissingFileRepairCard from './MissingFileRepairCard.vue'
-import VideoDedupCard from './VideoDedupCard.vue'
-import GatedPurgeCard from './GatedPurgeCard.vue'
 import BackupCard from './BackupCard.vue'
 import { useSystemActivityStore } from '../../stores/systemActivity.js'