chore: add Docker build configuration

Add multi-stage Dockerfile and nginx configuration:

**Dockerfile**
- Stage 1: Build with Node.js 22 Alpine and pnpm 9
- Stage 2: Serve with nginx 1.27 Alpine
- Static export optimization
- Health check endpoint

**nginx.conf**
- Gzip compression for assets
- CORS headers for Canvas API
- Cache static assets (1 year)
- Don't cache HTML files
- Support for WebAssembly files
- Security headers
- Client max body size: 100M for large image uploads

Ready for containerized deployment.

🤖 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://127.0.0.1/ || exit 1
+
+# Start nginx
+CMD ["nginx", "-g", "daemon off;"]

nginx.conf

@@ -0,0 +1,94 @@
+user nginx;
+worker_processes auto;
+error_log /var/log/nginx/error.log warn;
+pid /var/run/nginx.pid;
+
+events {
+    worker_connections 1024;
+}
+
+http {
+    include /etc/nginx/mime.types;
+    default_type application/octet-stream;
+
+    # Logging
+    log_format main '$remote_addr - $remote_user [$time_local] "$request" '
+                    '$status $body_bytes_sent "$http_referer" '
+                    '"$http_user_agent" "$http_x_forwarded_for"';
+    access_log /var/log/nginx/access.log main;
+
+    # Performance
+    sendfile on;
+    tcp_nopush on;
+    tcp_nodelay on;
+    keepalive_timeout 65;
+    types_hash_max_size 2048;
+    client_max_body_size 100M;
+
+    # Gzip compression
+    gzip on;
+    gzip_vary on;
+    gzip_proxied any;
+    gzip_comp_level 6;
+    gzip_types text/plain text/css text/xml text/javascript
+               application/json application/javascript application/xml+rss
+               application/rss+xml font/truetype font/opentype
+               application/vnd.ms-fontobject image/svg+xml;
+
+    # 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;
+    add_header Referrer-Policy "no-referrer-when-downgrade" always;
+
+    # Server block
+    server {
+        listen 80;
+        server_name _;
+        root /usr/share/nginx/html;
+        index index.html;
+
+        # Enable CORS for Canvas API (if needed)
+        add_header Access-Control-Allow-Origin "*" always;
+        add_header Access-Control-Allow-Methods "GET, POST, OPTIONS" always;
+        add_header Access-Control-Allow-Headers "DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range" always;
+
+        # Handle SPA routing
+        location / {
+            try_files $uri $uri/ /index.html;
+        }
+
+        # Cache static assets
+        location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot|webp)$ {
+            expires 1y;
+            add_header Cache-Control "public, immutable";
+        }
+
+        # Don't cache HTML files
+        location ~* \.html$ {
+            expires -1;
+            add_header Cache-Control "no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0";
+        }
+
+        # Handle WebAssembly files (for future image processing)
+        location ~* \.wasm$ {
+            types { application/wasm wasm; }
+            expires 1y;
+            add_header Cache-Control "public, immutable";
+        }
+
+        # Health check endpoint
+        location /health {
+            access_log off;
+            return 200 "healthy\n";
+            add_header Content-Type text/plain;
+        }
+
+        # Deny access to hidden files
+        location ~ /\. {
+            deny all;
+            access_log off;
+            log_not_found off;
+        }
+    }
+}