feat: refactor nxmesh-frontend to use React Router with new layout components

- Updated package.json to replace Vite with React Router for development and build scripts.
- Added react-router.config.ts for configuration settings.
- Created a new App component with a dashboard layout including header, sidebar, and footer.
- Enhanced App.css with a professional theme and responsive design.
- Removed old App.tsx and index.css files.
- Introduced RootLayout component to encapsulate layout structure.
- Developed Header, Footer, and Sidebar components for consistent layout.
- Implemented routes for home and dashboard with key metrics and activity sections.
- Updated vite.config.ts to integrate React Router and adjust SSR settings.

apps/nxmesh-frontend/src/components/layout/Header.tsx

@@ -0,0 +1,47 @@
+import { Space, Avatar, Input, Button, Badge, Dropdown, Layout, type DropdownProps } from 'antd';
+import { UserOutlined, SearchOutlined, BellOutlined, LogoutOutlined } from '@ant-design/icons';
+const { Header } = Layout;
+
+const userMenuItems: Exclude<DropdownProps['menu'], undefined>['items'] = [
+  { key: 'profile', label: 'Profile' },
+  { key: 'settings', label: 'Settings' },
+  { type: 'divider' },
+  { key: 'logout', label: 'Logout', icon: <LogoutOutlined /> },
+];
+
+export const LayoutHeader = () => {
+  return (
+    <Header
+      style={{
+        background: '#fff',
+        padding: '0 24px',
+        boxShadow: '0 2px 8px rgba(0, 0, 0, 0.06)',
+        display: 'flex',
+        justifyContent: 'space-between',
+        alignItems: 'center',
+        position: 'sticky',
+        top: 0,
+        zIndex: 999,
+      }}
+    >
+      <div style={{ display: 'flex', alignItems: 'center', gap: '16px' }}>
+        <h1 style={{ margin: 0, fontSize: '20px', fontWeight: 'bold', color: '#1890ff' }}>nxMesh</h1>
+      </div>
+
+      <Input placeholder="Search agents, workspaces..." prefix={<SearchOutlined />} style={{ width: '300px' }} />
+
+      <Space size="large">
+        <Badge count={3} style={{ backgroundColor: '#ff4d4f' }}>
+          <Button type="text" icon={<BellOutlined style={{ fontSize: '18px' }} />} />
+        </Badge>
+        <Dropdown menu={{ items: userMenuItems }} trigger={['click']}>
+          <Space style={{ cursor: 'pointer' }}>
+            <Avatar icon={<UserOutlined />} style={{ backgroundColor: '#1890ff' }} />
+            {/* TODO: from store */}
+            <span>Admin User</span>
+          </Space>
+        </Dropdown>
+      </Space>
+    </Header>
+  );
+};