品牌真正接入全站渲染 + document.title 同步 + 设置页实时刷新

- BrandContext 全局上下文: 挂载时拉取 GET /api/settings/brand
- HomePage: 品牌名称/标语/Logo 动态渲染, 封面卡片精调
- AdminLayout: 侧栏品牌名称/顶栏标语动态显示
- LoginPage: 登录页品牌 Logo + 名称
- WatchPage: 播放页接入品牌上下文
- Settings: 保存后调用 refresh() 全站即时刷新
- App.tsx: document.title 跟随 brand_name 变化
- 组件分层: AppRoutes + BrandProvider 避免 import 循环

frontend/src/App.tsx

@@ -3,6 +3,7 @@ import { BrowserRouter, Routes, Route, Navigate } from 'react-router-dom'
 import { ConfigProvider } from 'antd'
 import zhCN from 'antd/locale/zh_CN'
 import theme from './theme/anthropic'
+import { BrandProvider, useBrand } from './brand/BrandContext'
 import AdminLayout from './admin/AdminLayout'
 import LoginPage from './admin/LoginPage'
 import Dashboard from './admin/pages/Dashboard'
@@ -29,27 +30,37 @@ function AdminGuard({ children }: { children: React.ReactNode }) {
   return <>{children}</>
 }
 
+function AppRoutes() {
+  const { brand } = useBrand()
+  useEffect(() => { document.title = brand.brand_name }, [brand.brand_name])
+  return (
+    <BrowserRouter>
+      <Routes>
+        <Route path="/watch/:id" element={<WatchPage />} />
+        <Route path="/admin/login" element={<LoginPage />} />
+        <Route path="/admin" element={
+          <AdminGuard>
+            <AdminLayout />
+          </AdminGuard>
+        }>
+          <Route index element={<Dashboard />} />
+          <Route path="streams" element={<StreamList />} />
+          <Route path="streams/new" element={<StreamForm />} />
+          <Route path="nodes" element={<NodeManager />} />
+          <Route path="settings" element={<SettingsPage />} />
+        </Route>
+        <Route path="/" element={<HomePage />} />
+      </Routes>
+    </BrowserRouter>
+  )
+}
+
 export default function App() {
   return (
     <ConfigProvider theme={theme} locale={zhCN}>
-      <BrowserRouter>
-        <Routes>
-          <Route path="/watch/:id" element={<WatchPage />} />
-          <Route path="/admin/login" element={<LoginPage />} />
-          <Route path="/admin" element={
-            <AdminGuard>
-              <AdminLayout />
-            </AdminGuard>
-          }>
-            <Route index element={<Dashboard />} />
-            <Route path="streams" element={<StreamList />} />
-            <Route path="streams/new" element={<StreamForm />} />
-            <Route path="nodes" element={<NodeManager />} />
-            <Route path="settings" element={<SettingsPage />} />
-          </Route>
-          <Route path="/" element={<HomePage />} />
-        </Routes>
-      </BrowserRouter>
+      <BrandProvider>
+        <AppRoutes />
+      </BrandProvider>
     </ConfigProvider>
   )
 }