feat(fc2b): Settings Maintenance tab

MaintenancePanel hosts: backfill + centroid recompute trigger cards,
the five suggestion-threshold sliders (autosave on slider release),
the allowlist table (inline editable min_confidence, delete), and the
alias table (mapping display, delete). Wired as a third Settings tab,
ML settings loaded lazily when the tab opens.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/views/SettingsView.vue

@@ -5,6 +5,7 @@
     <v-tabs v-model="tab" color="accent" class="mb-4">
       <v-tab value="overview">Overview</v-tab>
       <v-tab value="import">Import</v-tab>
+      <v-tab value="maintenance">Maintenance</v-tab>
     </v-tabs>
 
     <v-window v-model="tab">
@@ -26,6 +27,10 @@
         <v-divider class="my-6" />
         <ImportTaskList />
       </v-window-item>
+
+      <v-window-item value="maintenance">
+        <MaintenancePanel />
+      </v-window-item>
     </v-window>
   </v-container>
 </template>
@@ -38,10 +43,13 @@ import SystemStatsCards from '../components/settings/SystemStatsCards.vue'
 import ImportTriggerPanel from '../components/settings/ImportTriggerPanel.vue'
 import ImportFiltersForm from '../components/settings/ImportFiltersForm.vue'
 import ImportTaskList from '../components/settings/ImportTaskList.vue'
+import MaintenancePanel from '../components/settings/MaintenancePanel.vue'
+import { useMLStore } from '../stores/ml.js'
 
 const tab = ref('overview')
 const system = useSystemStore()
 const importStore = useImportStore()
+const mlStore = useMLStore()
 
 let pollId = null
 
@@ -72,6 +80,8 @@ watch(tab, (t) => {
   if (t === 'import') {
     importStore.refreshStatus()
     importStore.loadTasks(true)
+  } else if (t === 'maintenance') {
+    mlStore.loadSettings()
   }
 })
 </script>