🎨 Palette: Explicit Empty State for High Score Onboarding

[EiJackGH]

💡 What: Implemented an explicit empty state for the personal best score. When highscore == 0, instead of rendering nothing, the game now displays: Personal Best: None yet! Go set a record!. Also appended a UX learning entry to .Jules/palette.md.
🎯 Why: To improve onboarding and clarity for first-time users. Explicit empty states provide helpful calls-to-action and make the UI's purpose clearer than simply hiding elements when data is absent.
📸 Before/After: Not applicable (terminal-based UI).
♿ Accessibility: Improves clarity of system state for new users.

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PR created automatically by Jules for task 12919874414959812278 started by @EiJackGH

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