feat(maintenance): DB maintenance UI card + fix ruff I001

- Settings → Maintenance gains a "Database maintenance" card: a "Run VACUUM
  ANALYZE now" button (enqueues the maintenance task) plus a per-table bloat
  readout (live/dead/dead%/last vacuum) from /api/admin/maintenance/db-stats.
- dbMaintenance store (loadStats / runVacuum) + test.
- Fix ruff I001: combine the two _sync_engine imports onto one line.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/settings/DbMaintenanceCard.vue

@@ -0,0 +1,84 @@
+<template>
+  <v-card>
+    <v-card-title>Database maintenance</v-card-title>
+    <v-card-text>
+      <p class="text-body-2 mb-3">
+        VACUUM (ANALYZE) reclaims dead-tuple bloat — which slows the random
+        showcase, since it samples physical blocks — and refreshes the query
+        planner's statistics. Runs automatically each week; trigger a pass
+        here after a large import or cleanup.
+      </p>
+      <v-btn color="primary" rounded="pill" :loading="busy" @click="run">
+        <v-icon start>mdi-database-cog</v-icon> Run VACUUM ANALYZE now
+      </v-btn>
+      <span v-if="queued" class="ml-3 text-caption text-success">Queued ✓</span>
+      <QueueStatusBar queue="maintenance" queue-label="Maintenance" />
+
+      <v-table
+        v-if="store.tables.length" density="compact" class="mt-4 fc-dbm__table"
+      >
+        <thead>
+          <tr>
+            <th>Table</th>
+            <th class="text-right">Live rows</th>
+            <th class="text-right">Dead</th>
+            <th class="text-right">Dead %</th>
+            <th>Last vacuum</th>
+          </tr>
+        </thead>
+        <tbody>
+          <tr v-for="t in store.tables" :key="t.table">
+            <td>{{ t.table }}</td>
+            <td class="text-right">{{ t.live.toLocaleString() }}</td>
+            <td class="text-right">{{ t.dead.toLocaleString() }}</td>
+            <td
+              class="text-right"
+              :class="{ 'text-warning': t.dead_pct >= 20 }"
+            >{{ t.dead_pct }}%</td>
+            <td class="text-caption">{{ fmt(t.last_vacuum || t.last_autovacuum) }}</td>
+          </tr>
+        </tbody>
+      </v-table>
+      <p v-else class="text-caption mt-3" style="opacity: 0.6;">
+        No table statistics yet.
+      </p>
+    </v-card-text>
+  </v-card>
+</template>
+
+<script setup>
+import { onMounted, ref } from 'vue'
+
+import { toast } from '../../utils/toast.js'
+import { useDbMaintenanceStore } from '../../stores/dbMaintenance.js'
+import QueueStatusBar from './QueueStatusBar.vue'
+
+const store = useDbMaintenanceStore()
+const busy = ref(false)
+const queued = ref(false)
+
+onMounted(() => store.loadStats())
+
+async function run () {
+  busy.value = true
+  queued.value = false
+  try {
+    await store.runVacuum()
+    queued.value = true
+    // pg_stat updates after the vacuum lands — refresh shortly after.
+    setTimeout(() => store.loadStats(), 5000)
+  } catch (e) {
+    toast({ text: e.message, type: 'error' })
+  } finally {
+    busy.value = false
+  }
+}
+
+function fmt (iso) {
+  return iso ? new Date(iso).toLocaleString() : '—'
+}
+</script>
+
+<style scoped>
+.fc-dbm__table { background: transparent; }
+</style>

frontend/src/components/settings/MaintenancePanel.vue

@@ -14,6 +14,7 @@
     <MLThresholdSliders class="mt-4" />
     <AllowlistTable class="mt-4" />
     <AliasTable class="mt-4" />
+    <DbMaintenanceCard class="mt-6" />
     <BackupCard class="mt-6" />
     <!-- TagMaintenanceCard moved to Cleanup tab (v26.05.25.7) — it
          operates on the existing library which fits the Cleanup-tab
@@ -31,6 +32,7 @@ import ThumbnailBackfillCard from './ThumbnailBackfillCard.vue'
 import MLThresholdSliders from './MLThresholdSliders.vue'
 import AllowlistTable from './AllowlistTable.vue'
 import AliasTable from './AliasTable.vue'
+import DbMaintenanceCard from './DbMaintenanceCard.vue'
 import BackupCard from './BackupCard.vue'
 import { useSystemActivityStore } from '../../stores/systemActivity.js'