🎨 Palette: Add keyboard instructions and accessibility

[EiJackGH]

💡 What

Added visible keyboard instructions under the score and included screen reader accessibility attributes (aria-live, aria-atomic) for dynamic score updates.

🎯 Why

Users were frequently unaware of what keys controlled Mario, and dynamic score updates were completely invisible to users relying on screen readers. This micro-improvement resolves both issues.

📸 Before/After

Before: Only the score text was shown, and users had to guess how to play. Screen readers would read the initial score but never announce changes.
After: A subtle semi-transparent instruction text reads "Press Space or Up Arrow to jump", and screen readers politely read the score updates dynamically as goombas are defeated.

♿ Accessibility

• Added aria-live="polite" and aria-atomic="true" to the #score div to ensure screen readers dynamically announce score changes without interrupting critical speech.
• Added visible text instructions in #instructions to ensure users know how to interact with the game.

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PR created automatically by Jules for task 12673838165355789364 started by @EiJackGH

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