[Feature] Add Restart Button Next to Pause/Resume in Pong Game

## 🎯 Feature Request
Currently, the game only has **Pause/Resume** functionality.
To improve usability, we can add a **Restart button** next to Pause/Resume, so the player can restart the game anytime without refreshing the page.

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## ✅ Tasks
- [ ] Add a Restart button in the game controls (UI).
- [ ] On click, reset ball position, scores, and paddle positions.
- [ ] Ensure Pause/Resume still works correctly after restart.
- [ ] Test in all difficulty modes.

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## 💡 Expected Outcome
Players will be able to restart the game anytime during play, improving the user experience.

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