🎨 Palette: Comma-formatted scores and enhanced achievement feedback

[aidasofialily-cmd]

💡 What: This PR introduces comma-formatting for all numeric scores and enhances the "New Personal Best" achievement feedback.

• A new header src/utils.hpp provides a formatWithCommas function.
• Scores in the HUD, initial personal best, and final score summary now use thousands-separators (e.g., 1,234 instead of 1234).
• The "NEW BEST!" message now includes the previous high score for context (e.g., NEW BEST! ✨🥳 (was 1,000)) and is highlighted in Bold Yellow.

🎯 Why: In a fast-paced "Speed Clicker" game, raw integers become difficult to parse quickly as they grow. Adding commas improves at-a-glance readability. Providing the previous high score context makes reaching a new milestone feel more tangible and rewarding.

♿ Accessibility: Improved readability of numeric information in the terminal UI.

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PR created automatically by Jules for task 14317595766223097071 started by @aidasofialily-cmd

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