Support OKLCH color scheme

[DropSnorz]

Summary

Add OKLCH in the Color Converter widget (src/widgets/color-converter/), alongside the existing HEX / RGB / HSL fields, following the same sync pattern already used for those.

Add a richer, dedicated OKLCH widget (L/C/H sliders, live sRGB/P3 gamut boundary warning, palette/scale generation)

References

• Add OKLab and OKLCH support omgovich/colord#87 — Add OKLab and OKLCH support (upstream, unmerged)
• src/widgets/color-converter/ColorConverterWidget.tsx
• src/widgets/color-converter/definition.ts