feat: implement RAG dashboard with MUI and react-router

Add new RAG dashboard feature including:
- Main application layout with header and sidebar
- Multiple pages (Home, KnowledgeBase, PipelineConfig, Dashboard, MCP)
- Theme configuration and styling
- Routing setup with protected routes
- Login page and authentication flow
- Various UI components and mock data for dashboard views

src/components/Layout/MainLayout.tsx

@@ -0,0 +1,39 @@
+import { Box, styled } from '@mui/material';
+import { Outlet } from 'react-router-dom';
+import Header from './Header';
+import Sidebar from './Sidebar';
+
+const LayoutContainer = styled(Box)({
+  display: 'flex',
+  height: '100vh',
+});
+
+const MainContent = styled(Box)({
+  flex: 1,
+  display: 'flex',
+  flexDirection: 'column',
+  overflow: 'hidden',
+});
+
+const ContentArea = styled(Box)({
+  flex: 1,
+  padding: '20px',
+  overflow: 'auto',
+  backgroundColor: '#f5f7fa',
+});
+
+const MainLayout = () => {
+  return (
+    <LayoutContainer>
+      <Sidebar />
+      <MainContent>
+        <Header />
+        <ContentArea>
+          <Outlet />
+        </ContentArea>
+      </MainContent>
+    </LayoutContainer>
+  );
+};
+
+export default MainLayout;