🎨 Implement toHsl() and use HSL as default color format

[Copilot]

Implements the toHsl() method that was throwing "not implemented" and changes the default color serialization from hex to HSL format.

Changes

• Color.toHsl(): Converts RGB to HSL using existing rgbToHsl utility
  • Returns hsl(H, S%, L%) for opaque colors
  • Returns hsla(H, S%, L%, A%) for colors with alpha (consistent with toRgb()/rgba() pattern)
• Color.toString(): Now returns HSL instead of hex

Example

const color = Color.from('#009edd');
color.toHsl();     // 'hsl(197, 100%, 43%)'
color.toHex();     // '#009edd' (still available)

const withAlpha = Color.fromValues(255, 0, 0, 128);
withAlpha.toHsl(); // 'hsla(0, 100%, 50%, 50%)'

Tests

Added Color.toHsl.test.ts covering primary colors, grayscale, custom colors, HSL roundtrip, and HSLA format.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• scarf.sh
  • Triggering command: /usr/local/bin/node node ./report.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>🎨 Use hsl</issue_title>
<issue_description>Use colors in hsl format (not rgb/hex/...)</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes 🎨 Use hsl #299

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