[ColorPicker] Support ref as prop, make input editable, and fix pointer events #607

Summary

Improvements to the ColorPicker component to add missing ref support and improve configurability.

Improvements

1. Missing ref prop support on multiple sub-components

ColorPickerRoot, ColorPickerArea, and ColorPickerInput don't accept ref as a prop.

2. ColorPickerInput is hardcoded readOnly

The input always renders as readOnly — users can't type in a hex/rgb value directly.

4. Manual pointer event handling in Area

ColorPickerArea manually manages pointermove/pointerup window event listeners. These should be cleaned up properly on unmount.

Moved to Cross-Cutting Issues

The following items have been moved to cross-cutting issues that address them across all components:

• Replace hardcoded CSS values with design tokens (Replace hardcoded CSS values with design tokens #672)