Update app.js with optimized code structure

[Mugunth140]

This optimized Express.js server configuration enhances scalability, readability, and professionalism by applying modern best practices. It includes middleware for handling CORS, cookie parsing, and request body parsing. Environment variables are cleanly managed using dotenv, keeping sensitive information secure. All API routes for users, appointments, medicines, cart management, payments, and testimonials are structured with clear paths, allowing for modular routing and future scalability. A default route ensures the server responds to base URL requests, and a global error handler is implemented to provide consistent and centralized error management. This setup is ideal for a production-ready application, designed for efficient backend API management.

[vercel[bot]]

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