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

src/pages/index.tsx

@@ -41,7 +41,7 @@ const Index: NextPage = () => {
           content="xevion, rdap, whois, rdap, domain name, dns, ip address"
         />
       </Head>
-      <nav className="bg-zinc-850 px-5 py-4 shadow-sm">
+      <nav className="bg-zinc-850 px-5 py-4 shadow-xs">
         <span
           className="text-xl font-medium text-white"
           style={{ fontSize: "larger" }}