feat: add layout components and pages for NxMesh Admin

- Implemented Header, Sidebar, and Layout components for consistent UI structure.
- Created pages for Agents, Certificates, Configurations, Dashboard, and Settings.
- Integrated React Query for data fetching in Agents, Certificates, Configurations, and Dashboard pages.
- Added Tailwind CSS for styling and responsive design.
- Established a utility function for conditional class names.
- Set up Vite configuration for React project with TypeScript support.
- Included global styles and Tailwind CSS configuration.

frontend/src/main.tsx

@@ -0,0 +1,18 @@
+import React from 'react'
+import ReactDOM from 'react-dom/client'
+import { BrowserRouter } from 'react-router-dom'
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import App from './App.tsx'
+import './styles/index.css'
+
+const queryClient = new QueryClient()
+
+ReactDOM.createRoot(document.getElementById('root')!).render(
+  <React.StrictMode>
+    <QueryClientProvider client={queryClient}>
+      <BrowserRouter>
+        <App />
+      </BrowserRouter>
+    </QueryClientProvider>
+  </React.StrictMode>,
+)