fix: add restart button after game over in Space Invaders

[Lonewolf2511]

PR Description 📜

Adds a "Restart" button and Game Over overlay (with final score) to the Space Invaders game. Previously, when the player lost, gameOver was set to true internally but nothing was shown to the user and there was no way to play again without manually reloading the page.

This PR is not tied to a filed issue — the missing restart functionality was found through a direct review of the codebase.

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[kunjgit]

Thank you @Lonewolf2511 ,for creating the PR and contributing to our GameZone 💗
Review team will review the PR and will reach out to you soon! 😇
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Thank you for your patience! 😀