chore: update dependencies and configuration for Tailwind CSS

- Added "@tailwindcss/postcss" to package.json dependencies.
- Updated "tailwindcss" version to "^4.3.0" in package.json.
- Modified postcss.config.mjs to use "@tailwindcss/postcss" instead of "tailwindcss".
- Changed darkMode configuration in tailwind.config.ts to a string format.

postcss.config.mjs

@@ -1,6 +1,6 @@
 const config = {
   plugins: {
-    tailwindcss: {},
+    "@tailwindcss/postcss": {},
     autoprefixer: {},
   },
 };