🎨 Palette: Add keyboard instructions and screen reader support to game

[EiJackGH]

💡 What:
Added visible keyboard instructions ("Press Space or ↑ to jump") to the game UI and improved the screen reader accessibility of the score counter.

🎯 Why:
When players land on an interactive HTML5 game like this Mario clone, it's not always obvious what keys map to actions, which can cause frustration. Providing clear, immediate instructions eliminates this friction.

📸 Before/After:

• Before: Game simply starts, no indication of how to jump. Score is silent to screen readers.
• After: A small, unintrusive semi-transparent block in the top right explicitly lists controls. The score dynamically announces its changes to assistive technologies.

♿ Accessibility:

• aria-live="polite" and aria-atomic="true" added to the #score element, ensuring screen readers announce score updates dynamically without interrupting other critical page flow.
• Ensure the instruction element remains visible to assistive tools by removing erroneous aria-hidden attributes.

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PR created automatically by Jules for task 328153760621158041 started by @EiJackGH

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