feat!: SPEC_2026, SchemeCmf, and PaletteStyle sealed interface

[jordond]

Summary

• Adds upstream SPEC_2026 color spec and SchemeCmf for the CMF (Color, Material, Finish) dual-source color scheme
• Converts PaletteStyle from an enum to a sealed interface — existing styles become data objects, Cmf becomes a @Poko class with an optional tertiarySourceColor: Color? parameter
• Users can now pass a second source color through the high-level Compose API (PaletteStyle.Cmf(tertiarySourceColor = Color.Blue)) instead of needing SchemeCmf directly
• Updates README with 4.x → 5.x migration guide, CMF usage docs, and SPEC_2026 info
• Notes that Material Expressive (5.0.0-alpha) moves to 6.x

Breaking changes

• PaletteStyle is a sealed interface, not an enum — PaletteStyle.entries / values() no longer exist
• PaletteStyle.Cmf is now a class (constructed with PaletteStyle.Cmf()) instead of an enum entry
• DynamicScheme constructor accepts sourceColorHctList (existing single-source constructors still work)

Test plan

• ./gradlew :material-kolor:jvmTest passes
• Verify API dump is correct for all targets
• Test CMF with single source and dual source colors in the demo app

[jordond]

Code review

Found 2 issues:

1. DynamicScheme(...) factory function loses sourceColorHctList when PaletteStyle.Cmf is used with palette overrides — the factory always calls the single-source constructor (sourceColorHct = seedColor.toHct()), collapsing sourceColorHctList to a 1-element list. ColorSpec2026.tertiary() and tertiaryContainer() read sourceColorHctList.getOrNull(1) for tone derivation and silently fall back to the primary source tone, discarding Cmf.tertiarySourceColor.

MaterialKolor/material-kolor/src/commonMain/kotlin/com/materialkolor/ktx/DynamicScheme.kt

Lines 172 to 187 in abef55d

	return DynamicScheme(
	sourceColorHct = seedColor.toHct(),
	variant = style.asVariant,
	isDark = isDark,
	contrastLevel = contrastLevel,
	primaryPalette = primary?.toTonalPalette() ?: defaults.primaryPalette,
	secondaryPalette = secondary?.toTonalPalette() ?: defaults.secondaryPalette,
	tertiaryPalette = tertiary?.toTonalPalette() ?: defaults.tertiaryPalette,
	neutralPalette = neutral?.toTonalPalette() ?: defaults.neutralPalette,
	neutralVariantPalette = neutralVariant?.toTonalPalette() ?: defaults.neutralVariantPalette,
	errorPalette = error?.toTonalPalette() ?: defaults.errorPalette,
	specVersion = specVersion,
	platform = platform,
	)
	}

2. High-level factory functions (toDynamicScheme, DynamicScheme(seedColor, ...)) default specVersion to ColorSpec.SpecVersion.Default which is SPEC_2021. Callers using PaletteStyle.Cmf() without explicitly passing specVersion = SPEC_2026 get an IllegalArgumentException from deep inside SchemeCmf.init with no guidance at the call site. PaletteStyle.Cmf KDoc documents the requirement, but neither factory function documents or guards it.

MaterialKolor/material-kolor/src/commonMain/kotlin/com/materialkolor/ktx/DynamicScheme.kt

Lines 139 to 155 in abef55d

	/**
	* Create a [DynamicScheme] based on the provided colors.
	*
	* If a color is not provided, then the color palette will be generated from the [style] and [seedColor].
	*
	* @param[seedColor] The color to base the scheme on.
	* @param[isDark] Whether the scheme should be dark or light.
	* @param[primary] The primary color of the scheme.
	* @param[secondary] The secondary color of the scheme.
	* @param[tertiary] The tertiary color of the scheme.
	* @param[neutral] The neutral color of the scheme.
	* @param[neutralVariant] The neutral variant color of the scheme.
	* @param[error] The error color of the scheme.
	* @param[style] The style of the scheme.
	* @param[contrastLevel] The contrast level of the scheme.
	* @param[specVersion] The version of the color specification to use.
	* @param[platform] The platform to use for the scheme.