feat: complete Vue UI parity (full backend + frontend)

== New domain models (7) ==
- UserPermission: per-user feature toggles (13 booleans)
- StorageConfig: encrypted Alist/S3/WebDAV adapters
- LicenseKey + LicenseActivation: offline license issuance
- DownloadClient: multi-client downloader configs
- AssistantSession + AssistantMessage: multi-turn AI chat persistence

== New services (5) ==
- PermissionService: admin grants always-true; user defaults seeded
- StorageConfigService: AES-GCM encryption + per-type connection probe
- LicenseService: 24-char hyphenated key generation, activation/heartbeat
- DownloadClientService: qB/Aria2/Transmission CRUD + WebUI test
- AssistantService: chat history + execute/undo stubs (op_id tracking)

== Extended AIService.Chat ==
- Multi-turn LLM call with chat history; offline fallback reply

== New endpoints (60+) ==
Auth:
  POST /auth/refresh, /auth/logout, /auth/change-password
  PATCH /auth/profile
  GET /auth/permissions, /auth/me

Permissions admin:
  GET/PUT /admin/users/:id/permissions
  POST /admin/users/:id/permissions/reset

Search:
  GET /search, /search/advanced, /search/tmdb, /search/sites

System:
  GET /system/config, /settings/schema, /system/events/ticket
  POST /admin/system/scheduler/:name/trigger

Stats:
  GET /stats/user/:id, /stats/top-users
  POST /stats/play

Sites:
  GET /sites/:id/resource, /sites/:id/userdata

Subscriptions:
  PUT /subscriptions/:id, POST /subscriptions/:id/search

Playlists:
  POST /playlists/:id/reorder
  DELETE /playlists/:id/items/by-id/:item_id

DLNA per-renderer:
  POST /dlna/:uuid/{play,pause,stop}, GET /dlna/:uuid/status

Media:
  POST/DELETE /media/:id/favorite, GET /media/:id/favorite/status
  POST /media/:id/ai-scrape, /media/scrape/test, /media/organize
  GET /favorites (alias)

Playback:
  GET /playback/:id/info, /playback/:id/external-players, /playback/:id/external-url
  POST /playback/:id/progress
  GET /playback/transcode/:job_id/status

Downloads:
  POST /download/:id/{pause,resume,organize}
  POST /download/{organize,sync,start-auto-sync}
  GET /download/tasks
  Admin: full CRUD on /admin/download/clients + /admin/download/aria2/stats

License:
  POST /license/{activate,heartbeat}
  GET /license/{status,heartbeat-status}
  Admin: /admin/license/{generate,list,:id/activations,:id/revoke,activation/:id/unbind}

Storage:
  GET /admin/storage/{status,:type}
  PUT /admin/storage/:type, POST /admin/storage/:type/test

Assistant (multi-turn AI):
  GET/POST /admin/assistant/sessions
  GET/DELETE /admin/assistant/session/:id
  POST /admin/assistant/{chat,execute}
  POST /admin/assistant/undo/:op_id
  GET /admin/assistant/history

== New React pages (4) ==
- AssistantChatPage (/assistant): full multi-turn chat UI with sessions
  sidebar, optimistic user-turn append, live AI response.
- DownloadClientsPage (/download-clients): typed CRUD form for
  qBittorrent / Aria2 / Transmission + per-row Test action.
- LicensePage (/license): generate keys, list activations, revoke,
  unbind individual devices.
- StorageConfigPage (/storage-config): tabbed Alist/WebDAV/S3 form
  with secret-aware redaction + connection probe.

== New API helpers (5) ==
- assistant, download_clients, license, permissions, storage_config

== Layout ==
- Sidebar gains 4 new admin links (AI 对话, 下载器, 外部存储, 许可证).

web/src/components/Layout.tsx

@@ -16,15 +16,19 @@ import {
   Heart,
   Home,
   KeyRound,
+  KeySquare,
   Link2,
   ListChecks,
   ListMusic,
   LogOut,
+  MessageSquare,
   Rss,
   Search,
+  Server,
   Settings,
   Sliders,
   Sparkles,
+  Cloud,
   Trash2,
   UserCog,
   Wrench,
@@ -118,6 +122,10 @@ export function Layout() {
               <SidebarLink to="/strm" icon={<Link2 size={18} />} label="STRM 管理" />
               <SidebarLink to="/tools" icon={<Wrench size={18} />} label="运维工具" />
               <SidebarLink to="/notify-channels" icon={<Bell size={18} />} label="通知渠道" />
+              <SidebarLink to="/download-clients" icon={<Server size={18} />} label="下载器" />
+              <SidebarLink to="/storage-config" icon={<Cloud size={18} />} label="外部存储" />
+              <SidebarLink to="/license" icon={<KeySquare size={18} />} label="许可证" />
+              <SidebarLink to="/assistant" icon={<MessageSquare size={18} />} label="AI 对话" />
               <SidebarLink to="/settings" icon={<Sliders size={18} />} label="系统设置" />
               <SidebarLink to="/recycle" icon={<Trash2 size={18} />} label="回收站" />
               <SidebarLink to="/admin" icon={<Settings size={18} />} label="管理后台" />