feat: Add combined Dockerfile for Swarm/Portainer deployment

- Create single Dockerfile that builds frontend and backend together
- Add nginx.conf for combined container (proxies to localhost)
- Update docker-compose.prod.yml for Swarm compatibility:
  - Use pre-built image instead of build directive
  - Replace restart with deploy.restart_policy
  - Single 'app' service instead of separate backend/frontend

Dockerfile

@@ -0,0 +1,72 @@
+# Build frontend
+FROM node:20-alpine AS frontend-builder
+
+WORKDIR /app/frontend
+
+# Configure npm to use legacy peer deps
+RUN npm config set legacy-peer-deps true
+
+COPY frontend/package*.json ./
+RUN npm ci
+
+COPY frontend/ ./
+RUN npm run build
+
+# Build backend and final image
+FROM node:20-alpine
+
+# Install MinIO client (detect architecture)
+RUN ARCH=$(uname -m | sed 's/x86_64/amd64/g' | sed 's/aarch64/arm64/g') && \
+    wget https://dl.min.io/client/mc/release/linux-${ARCH}/mc && \
+    chmod +x mc && \
+    mv mc /usr/local/bin/
+
+# Install nginx for serving frontend
+RUN apk add --no-cache nginx
+
+WORKDIR /app
+
+# Copy backend package files
+COPY backend/package*.json ./
+
+# Install build tools for native dependencies
+RUN apk add --no-cache python3 make g++
+
+# Install production dependencies
+RUN npm ci --only=production
+
+# Rebuild bcrypt
+RUN npm rebuild bcrypt --build-from-source
+
+# Copy backend application files
+COPY backend/ ./
+
+# Copy frontend build
+COPY --from=frontend-builder /app/frontend/build /app/public
+
+# Copy nginx config for combined container
+COPY nginx.conf /etc/nginx/http.d/default.conf
+
+# Create non-root user
+RUN addgroup -g 1001 -S nodejs && \
+    adduser -S nodejs -u 1001
+
+# Create necessary directories with proper permissions
+RUN mkdir -p logs temp /tmp/minio-webui-temp /run/nginx && \
+    chown -R nodejs:nodejs /app logs temp /tmp/minio-webui-temp && \
+    chown -R nodejs:nodejs /var/lib/nginx /var/log/nginx /run/nginx
+
+# Create startup script
+RUN echo '#!/bin/sh' > /app/start.sh && \
+    echo 'nginx' >> /app/start.sh && \
+    echo 'exec node src/app.js' >> /app/start.sh && \
+    chmod +x /app/start.sh
+
+# Switch to non-root user
+USER nodejs
+
+# Expose ports (3000 for API, 80 for frontend)
+EXPOSE 3000 80
+
+# Start both nginx and node
+CMD ["/app/start.sh"]