feat: Upgrade to Tailwind CSS v4.1.18

- Migrate from tailwindcss v3.3 to v4.1.18
- Replace @tailwind directives with @import 'tailwindcss'
- Move custom colors to @theme block in globals.css
- Convert custom utilities to @utility syntax
- Update PostCSS config to use @tailwindcss/postcss
- Remove autoprefixer (now built-in)

src/components/DramOfTheDay.tsx

@@ -55,7 +55,7 @@ export default function DramOfTheDay({ bottles }: DramOfTheDayProps) {
             </button>
 
             {suggestion && (
-                <div className="fixed inset-0 z-[100] flex items-center justify-center p-6 bg-zinc-950/80 backdrop-blur-sm animate-in fade-in duration-300">
+                <div className="fixed inset-0 z-100 flex items-center justify-center p-6 bg-zinc-950/80 backdrop-blur-xs animate-in fade-in duration-300">
                     <div className="bg-zinc-900 w-full max-w-sm rounded-[40px] p-8 shadow-2xl border border-orange-500/20 relative animate-in zoom-in-95 duration-300">
                         <button
                             onClick={() => setSuggestion(null)}