Add Docker-based production deployment

- Multi-stage Dockerfile with Node builder and nginx server
- Nginx configuration with gzip, security headers, and caching
- Docker Compose setup with health checks
- Updated README with deployment instructions

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

nginx.conf

@@ -0,0 +1,31 @@
+server {
+    listen 80;
+    server_name _;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Gzip compression
+    gzip on;
+    gzip_vary on;
+    gzip_min_length 1024;
+    gzip_types text/plain text/css text/xml text/javascript application/javascript application/x-javascript application/xml+rss;
+
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header X-XSS-Protection "1; mode=block" always;
+
+    # Cache static assets
+    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+
+    # Serve index.html for all routes (SPA support)
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    # Error pages
+    error_page 404 /index.html;
+}