Build a Full-Stack Smart Classroom Timer Web App

Build me a complete full-stack web app for a smart, interactive classroom timer, designed for teachers in the classroom. The app must be in Arabic and have an easy-to-use interface on a large screen. Core features: 1- Countdown timer: The main function is a timer that allows the teacher to set the class period (default 45 minutes). There must be a progress bar or a circle that changes color based on remaining time (green, yellow, red). 2- Interactive sounds: Add a sound system linked to specific events: 3- Class start chime: A calm and attractive sound. 4- Last minute warning: A light "tick tock" sound or a small bell. 5- Time's up: A clear and distinctive bell sound. 6- Motivational sounds (library): Add buttons to play ready-made sounds like real applause, a success chime (ding), a gentle error sound, and short music for competitions. The teacher must control the volume (mute/unmute). 7- Class interaction tools: Add a button for "random student picker" from a list (the teacher can enter student names). When pressed, the student's name appears with a suspense sound. 7- Stage customization: Allow the teacher to add segments to the class (e.g., warm-up 5 minutes, discussion 10 minutes, exercise 15 minutes) and run a timer for each stage separately. Technical features: 1- Make the app responsive to work on large screens in the classroom. 2- Use a simple and modern design, with clear Arabic fonts and eye-friendly colors. 3- The app must be deployable directly by you. Based on this request, start by creating a detailed development plan, then start building.