feat: initialize Next.js 16 project with Tailwind CSS 4 and Docker support

Phase 1 Implementation:
- Set up Next.js 16 with React 19, TypeScript 5, and Turbopack
- Configure Tailwind CSS 4 with OKLCH color system
- Implement dark/light theme support
- Create core UI components: Button, Card, Slider, Progress, Toast
- Add ThemeToggle component for theme switching
- Set up project directory structure for audio editor
- Create storage utilities for settings management
- Add Dockerfile with multi-stage build (Node + nginx)
- Configure nginx for static file serving with caching
- Add docker-compose.yml for easy deployment
- Configure static export mode for production

Tech Stack:
- Next.js 16 with Turbopack
- React 19
- TypeScript 5
- Tailwind CSS 4
- pnpm 9.0.0
- nginx 1.27 (for Docker deployment)

Build verified and working ✓

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

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

components/ui/Button.tsx

@@ -0,0 +1,47 @@
+import * as React from 'react';
+import { cn } from '@/lib/utils/cn';
+
+export interface ButtonProps
+  extends React.ButtonHTMLAttributes<HTMLButtonElement> {
+  variant?: 'default' | 'destructive' | 'outline' | 'secondary' | 'ghost' | 'link';
+  size?: 'default' | 'sm' | 'lg' | 'icon';
+}
+
+const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
+  ({ className, variant = 'default', size = 'default', ...props }, ref) => {
+    return (
+      <button
+        className={cn(
+          'inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-md text-sm font-medium transition-colors',
+          'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2',
+          'disabled:pointer-events-none disabled:opacity-50',
+          {
+            'bg-primary text-primary-foreground hover:bg-primary/90':
+              variant === 'default',
+            'bg-destructive text-destructive-foreground hover:bg-destructive/90':
+              variant === 'destructive',
+            'border border-input bg-background hover:bg-accent hover:text-accent-foreground':
+              variant === 'outline',
+            'bg-secondary text-secondary-foreground hover:bg-secondary/80':
+              variant === 'secondary',
+            'hover:bg-accent hover:text-accent-foreground': variant === 'ghost',
+            'text-primary underline-offset-4 hover:underline': variant === 'link',
+          },
+          {
+            'h-10 px-4 py-2': size === 'default',
+            'h-9 rounded-md px-3': size === 'sm',
+            'h-11 rounded-md px-8': size === 'lg',
+            'h-10 w-10': size === 'icon',
+          },
+          className
+        )}
+        ref={ref}
+        {...props}
+      />
+    );
+  }
+);
+
+Button.displayName = 'Button';
+
+export { Button };