Add DevSecOpsApp code with updated Jenkins pipeline for multi-environment deployment

backend/Dockerfile

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+# Simple Node.js backend Dockerfile
+FROM node:18-alpine
+
+# Set working directory
+WORKDIR /app
+
+# Create a non-root user
+RUN addgroup -g 1001 -S nodejs && \
+    adduser -S nodeapp -u 1001
+
+# Copy package files
+COPY package*.json ./
+
+# Install dependencies
+RUN npm ci --only=production && npm cache clean --force
+
+# Copy application files
+COPY server.js ./
+
+# Create logs directory and set permissions
+RUN mkdir -p logs && chown -R nodeapp:nodejs /app
+
+# Switch to non-root user
+USER nodeapp
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+  CMD wget --no-verbose --tries=1 --spider http://localhost:3001/health || exit 1
+
+# Expose port
+EXPOSE 3001
+
+# Start the application
+CMD ["node", "server.js"]