Refactor code structure for improved readability and maintainability

src/App.tsx

@@ -0,0 +1,13 @@
+import '@mantine/core/styles.css';
+
+import { MantineProvider } from '@mantine/core';
+import { Router } from './Router';
+import { theme } from './theme';
+
+export default function App() {
+  return (
+    <MantineProvider theme={theme}>
+      <Router />
+    </MantineProvider>
+  );
+}