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/components/settings/AliasTable.vue

@@ -0,0 +1,43 @@
+<template>
+  <v-card>
+    <v-card-title>Tag aliases ({{ store.rows.length }})</v-card-title>
+    <v-data-table-virtual
+      :headers="headers" :items="store.rows" :loading="store.loading"
+      height="360" density="compact"
+      no-data-text="No aliases yet — create one from a suggestion's ⋮ menu."
+    >
+      <template #item.mapping="{ item }">
+        <code>{{ item.alias_string }}</code>
+        <span class="mx-2">→</span>
+        <strong>{{ item.canonical_tag_name }}</strong>
+      </template>
+      <template #item.actions="{ item }">
+        <v-btn
+          icon="mdi-delete" size="x-small" variant="text" color="error"
+          @click="store.remove(item.alias_string, item.alias_category)"
+        />
+      </template>
+    </v-data-table-virtual>
+  </v-card>
+</template>
+
+<script setup>
+import { onMounted } from 'vue'
+import { useAliasesStore } from '../../stores/aliases.js'
+
+const store = useAliasesStore()
+const headers = [
+  { title: 'Mapping', key: 'mapping', sortable: false },
+  { title: 'Category', key: 'alias_category', sortable: true, width: 130 },
+  { title: '', key: 'actions', sortable: false, width: 60 }
+]
+onMounted(() => store.load())
+</script>
+
+<style scoped>
+code {
+  background: rgb(var(--v-theme-surface-light));
+  padding: 1px 6px; border-radius: 4px;
+  font-family: 'JetBrains Mono', monospace;
+}
+</style>