Add Game Mode Selection Screen

I would like to propose a **Game Mode Selection Screen** to enhance the player experience by offering different gameplay styles.

On page load, the user will be presented with a screen to choose between 3 different game modes:

1. **Classic Mode** – Traditional Pong game with fixed AI speed.
2. **Time Attack** – 60 seconds countdown mode to score as much as possible.
3. **AI Chaos** – AI speed randomly changes during the game.

Once a mode is selected, the game starts accordingly and adapts the logic based on the selected mode.

I would like to work on this issue @Akki-jaiswal