feat: change date picker contrast

[tibisabau]

Description

Improved the contrast between active and inactive dates within the same month in the Date-Picker component to enhance accessibility and usability. The previous implementation used a disabled color token with full opacity, resulting in insufficient visual distinction between selectable and non-selectable dates.

The solution reduces the opacity of inactive (disabled) dates from 1.0 to 0.4 while using the standard text color. This creates a clear visual hierarchy where active dates appear at full opacity with the standard color, while inactive dates appear significantly lighter (40% opacity). This approach ensures WCAG compliance and works consistently across both light and dark themes since opacity is relative to the background.

Closes #2436.

Checklist if Applicable

• The tests passed – no tests required for CSS-only changes
• Linting passed – yarn lint and yarn format executed successfully in packages/components
• Documentation has been added
• CHANGELOG.md has been updated

[Copilot]

Pull request overview

This PR improves accessibility in the Date-Picker component by enhancing the visual contrast between active and inactive dates within the same month. The change addresses issue #2436 by modifying the styling of disabled dates to make them more distinguishable from selectable dates.

Changes:

• Modified disabled date styling to use reduced opacity (0.4) with standard text color instead of the disabled color token at full opacity
• This creates clearer visual hierarchy while maintaining WCAG compliance across light and dark themes

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