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/styles/index.css

@@ -0,0 +1,36 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+:root {
+  font-family: Inter, system-ui, Avenir, Helvetica, Arial, sans-serif;
+  line-height: 1.5;
+  font-weight: 400;
+
+  color-scheme: light dark;
+  color: rgba(255, 255, 255, 0.87);
+  background-color: #242424;
+
+  font-synthesis: none;
+  text-rendering: optimizeLegibility;
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+
+body {
+  margin: 0;
+  display: flex;
+  min-width: 320px;
+  min-height: 100vh;
+}
+
+#root {
+  width: 100%;
+}
+
+@media (prefers-color-scheme: light) {
+  :root {
+    color: #213547;
+    background-color: #ffffff;
+  }
+}