Date Picker: Fixes a few usability / accessibility issues

[coliff]

Description

Fixes:

• The disabled buttons should not have hover states - let's add pointer-events: none CSS
• The title could have role="header"
• The calendar dates can have type="button" (fixes this Webhint warning: https://webhint.io/docs/user-guide/hints/hint-button-type)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• https://deploy-preview-2344--moduswebcomponents.netlify.app/?path=/story/user-inputs-date-picker--default-with-picker

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[netlify]

✅ Deploy Preview for moduswebcomponents ready!

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Lighthouse	1 paths audited Performance: 27 (no change from production) Accessibility: 98 (no change from production) Best Practices: 92 (no change from production) SEO: 92 (no change from production) PWA: - View the detailed breakdown and full score reports

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