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/pages/DownloadClientsPage.tsx

@@ -0,0 +1,334 @@
+import { FormEvent, useEffect, useState } from 'react'
+import { Loader2, Pencil, Plus, Send, Server, Trash2 } from 'lucide-react'
+import toast from 'react-hot-toast'
+
+import {
+  downloadClientsAPI,
+  type DownloadClient,
+  type DownloadClientInput,
+  type DownloadClientType,
+} from '../api/download_clients'
+
+// DownloadClientsPage manages multiple downloader integrations.
+// Replaces the Vue UI's DownloadView "clients" tab with a typed CRUD
+// surface and a per-client Test button.
+export function DownloadClientsPage() {
+  const [clients, setClients] = useState<DownloadClient[]>([])
+  const [loading, setLoading] = useState(true)
+  const [editing, setEditing] = useState<DownloadClient | null>(null)
+  const [showForm, setShowForm] = useState(false)
+
+  const refresh = async () => {
+    setLoading(true)
+    try {
+      setClients(await downloadClientsAPI.list())
+    } finally {
+      setLoading(false)
+    }
+  }
+
+  useEffect(() => {
+    refresh().catch(() => undefined)
+  }, [])
+
+  const onTest = async (id: string) => {
+    try {
+      const r = await downloadClientsAPI.test(id)
+      if (r.ok) toast.success('连接成功')
+      else toast.error(r.error ?? '连接失败')
+    } catch (err: unknown) {
+      const msg =
+        (err as { response?: { data?: { error?: string } } })?.response?.data?.error ??
+        '测试失败'
+      toast.error(msg)
+    }
+  }
+
+  const onDelete = async (c: DownloadClient) => {
+    if (!confirm(`确定删除「${c.name}」?`)) return
+    try {
+      await downloadClientsAPI.remove(c.id)
+      toast.success('已删除')
+      await refresh()
+    } catch (err: unknown) {
+      const msg =
+        (err as { response?: { data?: { error?: string } } })?.response?.data?.error ??
+        '删除失败'
+      toast.error(msg)
+    }
+  }
+
+  return (
+    <div className="space-y-6">
+      <div className="flex items-center justify-between">
+        <div className="flex items-center gap-3">
+          <div className="flex h-10 w-10 items-center justify-center rounded-xl bg-cyan-400/10 text-cyan-300">
+            <Server size={20} />
+          </div>
+          <div>
+            <h1 className="font-display text-3xl font-bold text-white">下载器管理</h1>
+            <p className="text-sm text-slate-400">
+              qBittorrent / Aria2 / Transmission · 多客户端 + 连接测试
+            </p>
+          </div>
+        </div>
+        <button
+          onClick={() => {
+            setEditing(null)
+            setShowForm(true)
+          }}
+          className="neon-button"
+        >
+          <Plus size={16} /> 添加下载器
+        </button>
+      </div>
+
+      {loading && (
+        <div className="flex justify-center py-12 text-slate-400">
+          <Loader2 className="animate-spin" />
+        </div>
+      )}
+
+      {!loading && clients.length === 0 && (
+        <div className="glass-panel py-12 text-center text-slate-400">暂无下载器</div>
+      )}
+
+      {!loading && clients.length > 0 && (
+        <div className="space-y-3">
+          {clients.map((c) => (
+            <div
+              key={c.id}
+              className="glass-panel flex items-center justify-between gap-3"
+            >
+              <div className="min-w-0">
+                <div className="flex items-center gap-2">
+                  <span className="font-medium text-white">{c.name}</span>
+                  <span className="rounded border border-white/10 bg-white/5 px-2 py-0.5 text-xs text-slate-400">
+                    {c.type}
+                  </span>
+                  {c.is_default && (
+                    <span className="rounded bg-primary-400/20 px-2 py-0.5 text-xs text-primary-400">
+                      默认
+                    </span>
+                  )}
+                  {!c.enabled && (
+                    <span className="rounded bg-slate-500/30 px-2 py-0.5 text-xs text-slate-300">
+                      已禁用
+                    </span>
+                  )}
+                </div>
+                <div className="mt-1 truncate text-xs text-slate-400">
+                  {c.url}
+                  {c.username && ` · ${c.username}`}
+                  {c.save_path && ` · ${c.save_path}`}
+                </div>
+              </div>
+              <div className="flex shrink-0 gap-2">
+                <button
+                  onClick={() => onTest(c.id)}
+                  className="rounded border border-white/10 px-2 py-1 text-xs text-slate-300 hover:border-primary-400/40 hover:text-primary-400"
+                >
+                  <Send size={12} className="inline" /> 测试
+                </button>
+                <button
+                  onClick={() => {
+                    setEditing(c)
+                    setShowForm(true)
+                  }}
+                  className="rounded border border-white/10 px-2 py-1 text-xs text-slate-300 hover:border-primary-400/40 hover:text-primary-400"
+                >
+                  <Pencil size={12} className="inline" /> 编辑
+                </button>
+                <button
+                  onClick={() => onDelete(c)}
+                  className="rounded border border-red-400/40 px-2 py-1 text-xs text-red-400 hover:bg-red-400/10"
+                >
+                  <Trash2 size={12} className="inline" /> 删除
+                </button>
+              </div>
+            </div>
+          ))}
+        </div>
+      )}
+
+      {showForm && (
+        <ClientFormModal
+          editing={editing}
+          onClose={() => setShowForm(false)}
+          onSaved={async () => {
+            setShowForm(false)
+            await refresh()
+          }}
+        />
+      )}
+    </div>
+  )
+}
+
+function ClientFormModal({
+  editing,
+  onClose,
+  onSaved,
+}: {
+  editing: DownloadClient | null
+  onClose: () => void
+  onSaved: () => void | Promise<void>
+}) {
+  const [form, setForm] = useState<DownloadClientInput>(() => ({
+    name: editing?.name ?? '',
+    type: editing?.type ?? 'qbittorrent',
+    url: editing?.url ?? '',
+    username: editing?.username ?? '',
+    password: '',
+    save_path: editing?.save_path ?? '',
+    is_default: editing?.is_default ?? false,
+    enabled: editing?.enabled ?? true,
+  }))
+  const [saving, setSaving] = useState(false)
+
+  const onSubmit = async (e: FormEvent) => {
+    e.preventDefault()
+    setSaving(true)
+    try {
+      if (editing) await downloadClientsAPI.update(editing.id, form)
+      else await downloadClientsAPI.create(form)
+      toast.success('已保存')
+      await onSaved()
+    } catch (err: unknown) {
+      const msg =
+        (err as { response?: { data?: { error?: string } } })?.response?.data?.error ??
+        '保存失败'
+      toast.error(msg)
+    } finally {
+      setSaving(false)
+    }
+  }
+
+  const update = <K extends keyof DownloadClientInput>(k: K, v: DownloadClientInput[K]) =>
+    setForm((f) => ({ ...f, [k]: v }))
+
+  const placeholder = (
+    {
+      qbittorrent: 'http://127.0.0.1:8080',
+      aria2: 'http://127.0.0.1:6800/jsonrpc',
+      transmission: 'http://127.0.0.1:9091/transmission/rpc',
+    } as Record<DownloadClientType, string>
+  )[form.type]
+
+  return (
+    <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/60 p-4 backdrop-blur-sm">
+      <div className="glass-panel w-full max-w-lg max-h-[90vh] overflow-y-auto">
+        <h2 className="mb-4 font-display text-xl font-semibold text-white">
+          {editing ? '编辑下载器' : '添加下载器'}
+        </h2>
+        <form onSubmit={onSubmit} className="space-y-4">
+          <Field label="名称">
+            <input
+              required
+              className="input-base"
+              value={form.name}
+              onChange={(e) => update('name', e.target.value)}
+            />
+          </Field>
+          <Field label="类型">
+            <select
+              className="input-base"
+              value={form.type}
+              onChange={(e) => update('type', e.target.value as DownloadClientType)}
+            >
+              <option value="qbittorrent">qBittorrent</option>
+              <option value="aria2">Aria2 (JSON-RPC)</option>
+              <option value="transmission">Transmission</option>
+            </select>
+          </Field>
+          <Field label="URL">
+            <input
+              required
+              className="input-base"
+              placeholder={placeholder}
+              value={form.url}
+              onChange={(e) => update('url', e.target.value)}
+            />
+          </Field>
+          {form.type !== 'aria2' && (
+            <>
+              <Field label="用户名">
+                <input
+                  className="input-base"
+                  value={form.username ?? ''}
+                  onChange={(e) => update('username', e.target.value)}
+                />
+              </Field>
+              <Field label={editing ? '密码 (留空保持不变)' : '密码'}>
+                <input
+                  type="password"
+                  className="input-base"
+                  value={form.password ?? ''}
+                  onChange={(e) => update('password', e.target.value)}
+                />
+              </Field>
+            </>
+          )}
+          {form.type === 'aria2' && (
+            <Field label="RPC Token (作为密码字段保存)">
+              <input
+                type="password"
+                className="input-base"
+                value={form.password ?? ''}
+                onChange={(e) => update('password', e.target.value)}
+              />
+            </Field>
+          )}
+          <Field label="默认保存路径">
+            <input
+              className="input-base"
+              value={form.save_path ?? ''}
+              onChange={(e) => update('save_path', e.target.value)}
+            />
+          </Field>
+          <div className="flex flex-wrap gap-4">
+            <label className="flex items-center gap-2 text-sm text-slate-300">
+              <input
+                type="checkbox"
+                className="h-4 w-4 accent-primary-400"
+                checked={form.is_default}
+                onChange={(e) => update('is_default', e.target.checked)}
+              />
+              设为默认
+            </label>
+            <label className="flex items-center gap-2 text-sm text-slate-300">
+              <input
+                type="checkbox"
+                className="h-4 w-4 accent-primary-400"
+                checked={form.enabled}
+                onChange={(e) => update('enabled', e.target.checked)}
+              />
+              启用
+            </label>
+          </div>
+          <div className="flex justify-end gap-2 pt-2">
+            <button
+              type="button"
+              onClick={onClose}
+              className="rounded border border-white/10 px-4 py-2 text-sm text-slate-300 hover:bg-white/5"
+            >
+              取消
+            </button>
+            <button type="submit" disabled={saving} className="neon-button">
+              {saving && <Loader2 size={16} className="animate-spin" />} 保存
+            </button>
+          </div>
+        </form>
+      </div>
+    </div>
+  )
+}
+
+function Field({ label, children }: { label: string; children: React.ReactNode }) {
+  return (
+    <label className="block">
+      <span className="mb-1 block text-sm text-slate-300">{label}</span>
+      {children}
+    </label>
+  )
+}