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/Card.tsx

@@ -0,0 +1,78 @@
+import * as React from 'react';
+import { cn } from '@/lib/utils/cn';
+
+const Card = React.forwardRef<
+  HTMLDivElement,
+  React.HTMLAttributes<HTMLDivElement>
+>(({ className, ...props }, ref) => (
+  <div
+    ref={ref}
+    className={cn(
+      'rounded-lg border border-border bg-card text-card-foreground shadow-sm',
+      className
+    )}
+    {...props}
+  />
+));
+Card.displayName = 'Card';
+
+const CardHeader = React.forwardRef<
+  HTMLDivElement,
+  React.HTMLAttributes<HTMLDivElement>
+>(({ className, ...props }, ref) => (
+  <div
+    ref={ref}
+    className={cn('flex flex-col space-y-1.5 p-6', className)}
+    {...props}
+  />
+));
+CardHeader.displayName = 'CardHeader';
+
+const CardTitle = React.forwardRef<
+  HTMLParagraphElement,
+  React.HTMLAttributes<HTMLHeadingElement>
+>(({ className, ...props }, ref) => (
+  <h3
+    ref={ref}
+    className={cn(
+      'text-2xl font-semibold leading-none tracking-tight',
+      className
+    )}
+    {...props}
+  />
+));
+CardTitle.displayName = 'CardTitle';
+
+const CardDescription = React.forwardRef<
+  HTMLParagraphElement,
+  React.HTMLAttributes<HTMLParagraphElement>
+>(({ className, ...props }, ref) => (
+  <p
+    ref={ref}
+    className={cn('text-sm text-muted-foreground', className)}
+    {...props}
+  />
+));
+CardDescription.displayName = 'CardDescription';
+
+const CardContent = React.forwardRef<
+  HTMLDivElement,
+  React.HTMLAttributes<HTMLDivElement>
+>(({ className, ...props }, ref) => (
+  <div ref={ref} className={cn('p-6 pt-0', className)} {...props} />
+));
+CardContent.displayName = 'CardContent';
+
+const CardFooter = React.forwardRef<
+  HTMLDivElement,
+  React.HTMLAttributes<HTMLDivElement>
+>(({ className, ...props }, ref) => (
+  <div
+    ref={ref}
+    className={cn('flex items-center p-6 pt-0', className)}
+    {...props}
+  />
+));
+CardFooter.displayName = 'CardFooter';
+
+export { Card, CardHeader, CardFooter, CardTitle, CardDescription, CardContent };