Enable ESLint no-require-imports rule

frontend/postcss.config.js

@@ -1,6 +1,9 @@
+import postcss from '@tailwindcss/postcss';
+import autoprefixer from 'autoprefixer';
+
 module.exports = {
   plugins: [
-    require('@tailwindcss/postcss'),
-    require('autoprefixer'),
+    postcss,
+    autoprefixer,
   ],
 };