feat: Add white and black text color options for digital widgets

[violetto-rose]

Summary

Adds pure White and Black text color options for both date and time in digital clock widgets (DigitalClockWidget and VerticalClockWidget), giving users high-contrast monochrome choices alongside dynamic Material You theme colors.

Closes #528

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Technical Details & Fixes

1. Direct Colors in TextColor:

   • Added White (Color.WHITE) and Black (Color.BLACK) to TextColor.kt with direct @ColorInt support so static colors are returned directly without needing theme attribute resolution.

2. Fix for Color.WHITE Application in RemoteViews:

   • Previously, DigitalClockWidget.kt and VerticalClockWidget.kt guarded setTextColor with if (timeColor != -1 && dateColor != -1) because -1 was used as a fallback sentinel when resolving theme attributes.
   • However, in Android ARGB format (32-bit signed int), pure White (0xFFFFFFFF) is literally -1 (Color.WHITE == -1), which caused pure white to be treated as an unresolved attribute and skipped.
   • Removed this check so direct colors (and standard theme attributes) are always applied as expected to the widget views.

3. Color Picker Contrast & Swatch Outlines:

   • Added subtle borders around color swatches in ClockWidgetConfig.kt so white swatches on light backgrounds and black swatches on dark/AMOLED backgrounds remain easily distinguishable.
   • Used luminance-based checkmark tinting so the selection indicator is always clearly visible on any swatch color.

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Verification

• ./gradlew assembleDebug passed
• Installed and tested on device (./gradlew installDebug)
• Verified White, Black, and dynamic theme colors apply correctly across DigitalClockWidget and VerticalClockWidget