feat: implement debug menu functionality for high score and coins

[Mr-Weather]

✅ PR Checklist

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• My PR title follows the format: type(scope): description (#issue) (scope and #issue optional)
• I used the correct type: feat, fix, refactor, docs, test, chore
• I reviewed my code and removed unnecessary debug logs or comments.
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📝 What does this PR do?

• Added SET HIGH SCORE button: reads and writes the high score save file directly, changes persist across game sessions
• Added SET COINS button: reads and writes the total coins save file directly, changes persist across game sessions
• Added input validation: clears field and shows error prompt when non-numeric input is entered

🔗 Related Issue

Link to the issue this PR addresses (if any)

• This PR fixes/closes: [Feature]: make it easier to test the game for developers with a kind of "debug menu" to bypass things jvondermarck/dinosaur-exploder#393
• This PR doesn’t address a specific issue.

📸 Screenshots / Demos (if applicable)

demo.mp4

💬 Extra Notes (Optional)

This debug menu is accessible only to developers via the -DdebugMenu=true launch flag, as specified in the issue. Changes to high score and coins persist to save files so developers can immediately test unlock conditions without grinding.

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