fix(build): Revert to ESM config without imports

- Renamed back to tailwind.config.js (ESM)
- Used export default with hardcoded Design OS palette
- This avoids both CJS/ESM interop issues and module resolution errors

frontend/tailwind.config.js

@@ -1,5 +1,5 @@
 /** @type {import('tailwindcss').Config} */
-module.exports = {
+export default {
     content: [
         "./index.html",
         "./src/**/*.{js,ts,jsx,tsx}",
@@ -209,5 +209,5 @@ module.exports = {
         },
     },
 },
-    plugins: [],
+plugins: [],
 }