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>

Dockerfile

@@ -0,0 +1,41 @@
+# Multi-stage build for Next.js static export
+
+# Stage 1: Build the application
+FROM node:22-alpine AS builder
+
+# Install pnpm
+RUN corepack enable && corepack prepare pnpm@9.0.0 --activate
+
+# Set working directory
+WORKDIR /app
+
+# Copy package files
+COPY package.json pnpm-lock.yaml* ./
+
+# Install dependencies
+RUN pnpm install --frozen-lockfile
+
+# Copy application files
+COPY . .
+
+# Build the Next.js application (static export)
+RUN pnpm build
+
+# Stage 2: Production server with nginx
+FROM nginx:1.27-alpine AS runner
+
+# Copy custom nginx configuration
+COPY nginx.conf /etc/nginx/nginx.conf
+
+# Copy built static files from builder stage
+COPY --from=builder /app/out /usr/share/nginx/html
+
+# Expose port 80
+EXPOSE 80
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+  CMD wget --quiet --tries=1 --spider http://localhost/ || exit 1
+
+# Start nginx
+CMD ["nginx", "-g", "daemon off;"]