🎨 Palette: Improve accessibility and instructions for game controls

[EiJackGH]

💡 What

Added visible instructions for keyboard controls ("Press Space or Up Arrow to jump") and improved the accessibility of the dynamic score display in the Mario game.

🎯 Why

Users previously had to guess the keyboard controls to jump, creating friction. Additionally, screen reader users were not notified when the score updated dynamically.

📸 Before/After

(See Playwright verification screenshots for visual layout confirmation)
Before: Score was not announced, and there were no control instructions.
After: Score updates are dynamically announced via ARIA live regions, and a small, semi-transparent instructional hint appears below the score.

♿ Accessibility

• Added aria-live="polite" and aria-atomic="true" to the #score div to ensure score updates are read aloud.
• Made the score font bold for slightly better readability.
• The new instructional hint is rendered in standard text without aria-hidden="true", ensuring it's available to all users.

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PR created automatically by Jules for task 11072360107009144513 started by @EiJackGH

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