🎨 Palette: Add explicit keyboard instructions and accessible score

[EiJackGH]

💡 What:

• Added explicit visible instructional text telling users how to jump.
• Separated the static "Score: " text from the dynamic score value.
• Added aria-live="polite" and aria-atomic="true" to the dynamic score element.

🎯 Why:

• Users need to know what controls to use to interact with the game.
• Screen readers were likely reading "Score: 1", "Score: 2" every time the score changed. By extracting the static text out of the aria-live region, the screen reader will only read the new number, significantly reducing auditory clutter.

📸 Before/After:
(Visual changes verified locally via Playwright screenshot)

• Text "Press Space or Up Arrow to jump" is now visible at the bottom of the game area.

♿ Accessibility:

• Improved screen reader experience for dynamic score updates.
• Ensured instructional text does not interfere with clicks by using pointer-events: none.

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PR created automatically by Jules for task 10864274430660785147 started by @EiJackGH

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