🎨 Palette: Highlight keyboard shortcuts

[EiJackGH]

💡 What: Wrapped keyboard instructions in semantic <kbd> tags with high-contrast styling.
🎯 Why: To make the game controls stand out more against the background and feel more intuitive and discoverable as interactive elements. Added custom CSS to match the file's existing pattern of an internal <style> block.
📸 Before/After: Instructions were plain text; now they look like physical keys.
♿ Accessibility: Uses the semantic <kbd> tag to indicate user input for screen readers and assistive tech.

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PR created automatically by Jules for task 12987923512774895648 started by @EiJackGH

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