feat: upgrade Tailwind CSS to v4.1.11

- Upgrade Tailwind CSS from 3.x to 4.x for latest features and performance
- Install @tailwindcss/postcss plugin for Tailwind CSS 4.0 compatibility
- Update CSS configuration to use new @import and @config syntax
- Update PostCSS configuration to use new plugin format
- Build working correctly with new Tailwind CSS engine

src/styles.css

@@ -1,3 +1,3 @@
-@tailwind base;
-@tailwind components;
-@tailwind utilities;
+@import "tailwindcss";
+
+@config "../tailwind.config.js";