refactor: migrate from MUI to Ant Design for layout and components

- Updated package.json to remove MUI dependencies and add Ant Design.
- Refactored App component to use Ant Design's Layout, Header, Footer, and Sidebar.
- Created new Footer, Header, and Sidebar components using Ant Design.
- Removed old Header component that used MUI.
- Updated Home component to use Ant Design's Typography and Button.
- Added global styles in index.less and theme styles in theme.less and layout.less.
- Removed MUI theme configuration and replaced it with Ant Design's theming.

frontend/src/index.less

@@ -0,0 +1,89 @@
+/* === Reset & base === */
+*,
+*::before,
+*::after {
+  box-sizing: border-box;
+  margin: 0;
+  padding: 0;
+}
+
+/* Smooth scrolling */
+html {
+  scroll-behavior: smooth;
+}
+
+/* Root background and typography (matches theme background + font) */
+body {
+  font-family: "Inter", "Roboto", "Helvetica", "Arial", sans-serif;
+  background-color: #f9f9f9; /* matches theme.palette.background.default */
+  color: #262626; /* matches theme.palette.text.primary */
+  line-height: 1.6;
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+
+/* Anchor defaults */
+a {
+  color: #1976d2; /* primary main */
+  text-decoration: none;
+  transition: color 0.2s ease-in-out;
+}
+
+a:hover {
+  color: #004ba0; /* primary dark */
+}
+
+/* === Scrollbar styling (WebKit browsers) === */
+::-webkit-scrollbar {
+  width: 10px;
+  height: 10px;
+}
+
+::-webkit-scrollbar-track {
+  background: #f0f0f0;
+}
+
+::-webkit-scrollbar-thumb {
+  background: #bfbfbf;
+  border-radius: 5px;
+}
+
+::-webkit-scrollbar-thumb:hover {
+  background: #737373;
+}
+
+/* === Utility classes === */
+
+/* Center container with padding */
+.container {
+  max-width: 1200px;
+  margin: 0 auto;
+  padding: 1rem;
+}
+
+/* Add subtle fade animation for route transitions */
+.fade-enter {
+  opacity: 0;
+  transform: translateY(10px);
+}
+
+.fade-enter-active {
+  opacity: 1;
+  transform: translateY(0);
+  transition: opacity 0.3s, transform 0.3s;
+}
+
+/* === Code blocks / preformatted text === */
+pre,
+code {
+  background-color: #f0f0f0;
+  color: #262626;
+  padding: 0.25rem 0.5rem;
+  border-radius: 4px;
+  font-family: "JetBrains Mono", "Fira Code", monospace;
+}
+
+/* === App container fix for fixed header === */
+main {
+  padding-top: 64px; /* matches MUI AppBar height */
+}