build: upgrade Tailwind CSS from v3 to v4

- Migrate from Tailwind CSS 3.x to 4.1.15
- Replace autoprefixer with @tailwindcss/postcss 4.1.15
- Update PostCSS configuration for Tailwind v4 compatibility
- Convert globals.scss to globals.css for CSS-first configuration
- Remove legacy tailwind.config.cjs in favor of CSS-based config
- Update all component imports to use new globals.css
- Remove old.tsx.disabled file

postcss.config.cjs

@@ -1,6 +1,5 @@
 module.exports = {
   plugins: {
-    tailwindcss: {},
-    autoprefixer: {},
+    '@tailwindcss/postcss': {},
   },
 };