feat: initialize Convert UI - browser-based file conversion app

- Add Next.js 16 with Turbopack and React 19
- Add Tailwind CSS 4 with OKLCH color system
- Implement FFmpeg.wasm for video/audio conversion
- Implement ImageMagick WASM for image conversion
- Add file upload with drag-and-drop
- Add format selector with fuzzy search
- Add conversion preview and download
- Add conversion history with localStorage
- Add dark/light theme support
- Support 22+ file formats across video, audio, and images

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/ui/Skeleton.tsx

@@ -0,0 +1,16 @@
+import { cn } from '@/lib/utils/cn';
+
+function Skeleton({ className, ...props }: React.HTMLAttributes<HTMLDivElement>) {
+  return (
+    <div
+      className={cn('animate-shimmer rounded-md bg-muted', className)}
+      style={{
+        backgroundImage: 'linear-gradient(90deg, transparent, rgba(255,255,255,0.1), transparent)',
+        backgroundSize: '200% 100%',
+      }}
+      {...props}
+    />
+  );
+}
+
+export { Skeleton };