refactor: enhance Storybook interaction testing and update DatePicker component

- Updated Storybook testing rules to focus on modern interaction testing patterns using play functions and @storybook/test utilities.
- Removed deprecated sleep function and improved the DatePicker story to utilize more precise user interactions.
- Simplified the Calendar component's structure and improved accessibility features.
- Removed unused CSS imports from main.css to streamline styles and focus on essential Tailwind CSS imports.

Author: jaruesink