fix: import @tailwindcss/postcss directly instead of string reference for Turbopack compatibility

Author: Copilot

postcss.config.mjs

@@ -1,5 +1,7 @@
+import tailwindcss from "@tailwindcss/postcss";
+
 const config = {
-  plugins: ["@tailwindcss/postcss"],
+  plugins: [tailwindcss],
 };
 
 export default config;