品牌化重构: StreamCore + 现代UI主题 + 英文界面

- 移除所有emoji (HomePage中的🎬改为VideoCameraOutlined图标)
- 主题重设计: 深蓝色系主色(#1E3A5F),系统sans-serif字体
  白色/浅灰背景,现代卡片阴影和圆角,完全去除复古感
- 首页移除管理入口,纯观众视角(渐变横幅+卡片列表)
- 统一品牌名称 StreamCore (替换LiveStream)
- 全部界面英文(antd默认locale,去除zhCN)
- 登录页渐变+卡片居中布局

frontend/src/admin/AdminLayout.tsx

@@ -15,11 +15,11 @@ const { Sider, Content, Header } = Layout
 const { Text } = Typography
 
 const menuItems = [
-  { key: '/admin', icon: <DashboardOutlined />, label: '概览' },
-  { key: '/admin/streams', icon: <VideoCameraOutlined />, label: '直播列表' },
-  { key: '/admin/streams/new', icon: <PlusOutlined />, label: '创建直播' },
-  { key: '/admin/nodes', icon: <CloudServerOutlined />, label: '边缘节点' },
-  { key: '/admin/settings', icon: <SettingOutlined />, label: '系统设置' },
+  { key: '/admin', icon: <DashboardOutlined />, label: 'Dashboard' },
+  { key: '/admin/streams', icon: <VideoCameraOutlined />, label: 'Streams' },
+  { key: '/admin/streams/new', icon: <PlusOutlined />, label: 'New Stream' },
+  { key: '/admin/nodes', icon: <CloudServerOutlined />, label: 'Nodes' },
+  { key: '/admin/settings', icon: <SettingOutlined />, label: 'Settings' },
 ]
 
 export default function AdminLayout() {
@@ -44,7 +44,7 @@ export default function AdminLayout() {
         onCollapse={setCollapsed}
         width={220}
         style={{
-          borderRight: '1px solid #E8E4DD',
+          borderRight: '1px solid #E8ECF1',
           background: '#FFFFFF',
         }}
       >
@@ -53,10 +53,16 @@ export default function AdminLayout() {
           display: 'flex',
           alignItems: 'center',
           justifyContent: 'center',
-          borderBottom: '1px solid #E8E4DD',
+          borderBottom: '1px solid #E8ECF1',
+          background: '#1E3A5F',
+          color: '#FFFFFF',
         }}>
-          <Text strong style={{ fontSize: collapsed ? 14 : 18, letterSpacing: -0.5 }}>
-            {collapsed ? 'LS' : 'LiveStream'}
+          <Text strong style={{
+            fontSize: collapsed ? 14 : 18,
+            letterSpacing: -0.5,
+            color: '#FFFFFF',
+          }}>
+            {collapsed ? 'SC' : 'StreamCore'}
           </Text>
         </div>
         <Menu
@@ -70,7 +76,7 @@ export default function AdminLayout() {
       <Layout>
         <Header style={{
           background: '#FFFFFF',
-          borderBottom: '1px solid #E8E4DD',
+          borderBottom: '1px solid #E8ECF1',
           display: 'flex',
           justifyContent: 'flex-end',
           alignItems: 'center',
@@ -81,7 +87,7 @@ export default function AdminLayout() {
             icon={<LogoutOutlined />}
             onClick={handleLogout}
           >
-            退出登录
+            Logout
           </Button>
         </Header>
         <Content style={{ padding: 32, overflow: 'auto' }}>