🎨 Palette: Highlight keyboard shortcuts with <kbd> tags

[EiJackGH]

💡 What: Wrapped keyboard shortcut instructions in semantic <kbd> tags and added physical key styling.
🎯 Why: Makes the instructions much clearer and more intuitive by visually distinguishing the required keys from regular text.
📸 Before/After: Before, it was just plain text "Press Space or ↑ to jump!". After, "Space" and "↑" look like actual physical keyboard keys.
♿ Accessibility: Uses the semantic <kbd> HTML element, which is the web standard for representing user input, improving the underlying structure of the document.

Note: I added custom CSS to the internal <style> block to style the <kbd> elements. While I generally avoid adding custom CSS, this specific .njk file doesn't use utility classes and relies entirely on an internal <style> block, so appending to it was the cleanest way to follow the existing pattern in the file.

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PR created automatically by Jules for task 793055037228884225 started by @EiJackGH

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