ตัวแปลงสี Hex เป็น HSL

Expand a 3-digit hex to 6 digits if needed (e.g. #abc → #aabbcc), then parse each pair: r = parseInt(hex[0..1], 16) / 255, similarly for g and b.

Then apply RGB-to-HSL: L = (max + min) / 2; S = d / (2 − max − min) if L > 0.5, else S = d / (max + min); hue from the dominant channel as in RGB-to-HSL.