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/common/MaintenanceTile.vue

@@ -0,0 +1,121 @@
+<!--
+  Compact, expandable maintenance/cleanup action tile. Collapsed it shows just an
+  icon + short title + one-line purpose, so a section of these tiles in a grid is
+  scannable at a glance; clicking the header expands the full controls / preview /
+  result UI inline (the operator opted for "compact tiles in a grid, detail on
+  expand", 2026-06-18, replacing the old long stack of full-width cards).
+
+  Usage: wrap a card's action body in the default slot; pass icon/title/blurb.
+  `destructive` tints the icon error-red for delete actions. `open` can be forced
+  (e.g. keep a running task's tile expanded). Keyboard accessible: the header is a
+  real <button> with aria-expanded + focus ring.
+-->
+<template>
+  <v-card class="fc-tile" :class="{ 'fc-tile--open': isOpen }">
+    <button
+      type="button"
+      class="fc-tile__head"
+      :aria-expanded="isOpen"
+      @click="toggle"
+    >
+      <v-icon
+        :icon="icon"
+        :color="destructive ? 'error' : 'accent'"
+        class="fc-tile__icon"
+      />
+      <span class="fc-tile__text">
+        <span class="fc-tile__title">{{ title }}</span>
+        <span class="fc-tile__blurb">{{ blurb }}</span>
+      </span>
+      <v-icon
+        :icon="isOpen ? 'mdi-chevron-up' : 'mdi-chevron-down'"
+        class="fc-tile__chev"
+      />
+    </button>
+    <v-expand-transition>
+      <div v-show="isOpen" class="fc-tile__body">
+        <slot />
+      </div>
+    </v-expand-transition>
+  </v-card>
+</template>
+
+<script setup>
+import { computed, ref, watch } from 'vue'
+
+const props = defineProps({
+  icon: { type: String, required: true },
+  title: { type: String, required: true },
+  blurb: { type: String, default: '' },
+  destructive: { type: Boolean, default: false },
+  // Force-open (e.g. a tile whose task is mid-run). When set, the operator can
+  // still collapse it locally, but a change to `open` re-applies.
+  open: { type: Boolean, default: false },
+})
+
+const local = ref(props.open)
+watch(() => props.open, (v) => { local.value = v })
+const isOpen = computed(() => local.value)
+
+function toggle() {
+  local.value = !local.value
+}
+</script>
+
+<style scoped>
+.fc-tile {
+  border-radius: 8px;
+  overflow: hidden;
+}
+.fc-tile__head {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  width: 100%;
+  padding: 12px 14px;
+  background: transparent;
+  border: none;
+  text-align: left;
+  cursor: pointer;
+  color: inherit;
+}
+.fc-tile__head:hover {
+  background: rgba(var(--v-theme-on-surface), 0.04);
+}
+.fc-tile__head:focus-visible {
+  outline: 2px solid rgb(var(--v-theme-accent));
+  outline-offset: -2px;
+}
+.fc-tile__icon {
+  flex: 0 0 auto;
+}
+.fc-tile__text {
+  display: flex;
+  flex-direction: column;
+  min-width: 0;
+  flex: 1 1 auto;
+}
+.fc-tile__title {
+  font-weight: 600;
+  font-size: 0.95rem;
+  line-height: 1.2;
+}
+.fc-tile__blurb {
+  font-size: 0.8rem;
+  line-height: 1.25;
+  color: rgb(var(--v-theme-on-surface-variant));
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.fc-tile--open .fc-tile__blurb {
+  white-space: normal;
+}
+.fc-tile__chev {
+  flex: 0 0 auto;
+  color: rgb(var(--v-theme-on-surface-variant));
+}
+.fc-tile__body {
+  padding: 0 14px 14px;
+}
+</style>