Add Docker support with Dockerfile, docker-compose, and deployment documentation

Dockerfile

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+# Use Node.js LTS
+FROM node:20-alpine
+
+# Install dependencies for native modules
+RUN apk add --no-cache python3 make g++
+
+# Create app directory
+WORKDIR /app
+
+# Copy package files
+COPY package*.json ./
+
+# Install dependencies
+RUN npm ci --only=production
+
+# Copy application code
+COPY . .
+
+# Create directories for data
+RUN mkdir -p /data/artwork /data/music
+
+# Expose port
+EXPOSE 4000
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+  CMD node -e "require('http').get('http://localhost:4000/health', (r) => {process.exit(r.statusCode === 200 ? 0 : 1)})"
+
+# Start the server
+CMD ["npm", "start"]