fix(SettingsDialog): drop dead imports after AI tab removal

tsc --noEmit caught seven TS6133 "declared but never used" + one
TS2614 "no exported member 'features'" left over from a27267f. Strip
Brain/RotateCcw icons, the unused Switch + Loader2 imports, the
adminApi + featuresApi + features module references, and the
SETTINGS_FEATURE_FLAGS_KEY constant. No runtime change.

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

frontend/src/components/dialogs/SettingsDialog.tsx

@@ -16,17 +16,13 @@ import {
   Activity,
   FolderSearch,
   Shield,
-  Brain,
-  RotateCcw,
   Trash2,
 } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import { useQuery, useQueryClient, useMutation } from '@tanstack/react-query'
 import {
   library,
-  admin as adminApi,
   account as accountApi,
-  features as featuresApi,
   nextcloud as nextcloudApi,
   type MediaType,
   type PipelineStage,
@@ -39,7 +35,6 @@ import { useAuth } from '../../contexts/AuthContext'
 import { UserManagement } from '../admin/UserManagement'
 import { NextcloudFolderPicker } from './NextcloudFolderPicker'
 import { Tabs, TabsList, TabsTrigger } from '@/components/ui/tabs'
-import { Switch } from '@/components/ui/switch'
 import { Button } from '@/components/ui/button'
 
 // React Query keys for the settings panels. Kept here (not in a shared
@@ -62,8 +57,6 @@ const TABS: { id: SettingsTab; label: string; adminOnly?: boolean }[] = [
   { id: 'users', label: 'Users', adminOnly: true },
 ]
 
-const SETTINGS_FEATURE_FLAGS_KEY = ['settings', 'feature-flags'] as const
-
 /**
  * Full-page settings view with tabbed navigation. Replaces the old
  * modal dialog — renders as a top-level section in the main content