I need a lean PHP build for a small e-commerce site. The first milestone is a working skeleton with two essentials: • Phone-number-based sign-up / sign-in using OTP, storing user profiles in MySQL. • A single payment gateway wired up end-to-end (Razorpay or Stripe—whichever you are most comfortable with). Beyond that, a simple home page and placeholder product area are enough; I mainly want to verify that the authentication flow and payment flow are rock-solid. Please keep the code clean, comment clearly, and use modern PHP practices (PHP 8+, prepared statements, minimal dependencies). If you can hand over a short README with setup steps and database schema, that will close the project.