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/BulkScanSheet.tsx

@@ -122,7 +122,7 @@ export default function BulkScanSheet({
                 className="fixed inset-0 bg-black z-50 flex flex-col"
             >
                 {/* Header */}
-                <div className="flex items-center justify-between p-4 bg-zinc-900/80 backdrop-blur-sm border-b border-zinc-800">
+                <div className="flex items-center justify-between p-4 bg-zinc-900/80 backdrop-blur-xs border-b border-zinc-800">
                     <div className="flex items-center gap-3">
                         <div className="w-10 h-10 rounded-xl bg-orange-600/20 flex items-center justify-center">
                             <Zap size={20} className="text-orange-500" />
@@ -240,7 +240,7 @@ export default function BulkScanSheet({
                                             <X size={12} className="text-white" />
                                         </button>
                                     )}
-                                    <span className="absolute bottom-0.5 left-0.5 text-[9px] font-bold text-white bg-black/60 px-1 rounded">
+                                    <span className="absolute bottom-0.5 left-0.5 text-[9px] font-bold text-white bg-black/60 px-1 rounded-sm">
                                         #{i + 1}
                                     </span>
                                 </motion.div>