🎨 Palette: Add keyboard controls hint and a11y score updates to Mario game

[EiJackGH]

💡 What:

• Added a visual keyboard shortcut hint ("Jump: Space or ↑") to the Mario game overlay.
• Added aria-live="polite" and aria-atomic="true" to the score counter.
• Made the score font bolder for better readability.
• Cleaned up the requirements.txt file by removing the broken venv entry to ensure smooth local test runs and CI checks.

🎯 Why:

• Intuitiveness: New players immediately know which keys to press without trial and error.
• Accessibility (Score): Screen reader users will now be politely notified as their score increments dynamically during gameplay.
• Project Health: Removing venv from the requirements file enables standard pip install -r requirements.txt commands to work without throwing errors.

📸 Before/After:

Before: Only the score was displayed, with no indication of controls.
After: A subtle, semi-transparent hint box sits below the score, providing clear gameplay instructions without obstructing the screen.

♿ Accessibility:

• The score dynamically updates using ARIA live regions.
• The control hint is visible to sighted users and automatically readable by screen readers as standard HTML content (no aria-hidden tricks used).

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PR created automatically by Jules for task 3782868735741987336 started by @EiJackGH

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