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>

lib/utils/cn.ts

@@ -0,0 +1,10 @@
+import { type ClassValue, clsx } from 'clsx';
+import { twMerge } from 'tailwind-merge';
+
+/**
+ * Merge Tailwind CSS classes with proper precedence
+ * Combines clsx for conditional classes and twMerge for Tailwind class deduplication
+ */
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs));
+}