Update BaseStyles.dev.stories.tsx to no longer use styled-components

[Copilot]

This PR migrates the BaseStyles.dev.stories.tsx file from using styled-components to CSS modules as part of the project's effort to move away from styled-components.

Changes Made

• Removed BaseStyles component usage from all stories and replaced with plain <div> elements
• Created BaseStyles.dev.stories.module.css with CSS classes that replicate the exact styling behavior of the original sx and system props
• Updated imports to include clsx for combining CSS classes and the new CSS module
• Migrated stories:
  • WithSxProps: Now uses CSS class instead of sx prop
  • WithSystemProps: Now uses CSS class instead of system props like color, backgroundColor, etc.
  • WithStyleProps: Already used inline styles, no changes needed
  • Default: No changes needed (returns plain text)

Visual Verification

All stories maintain their exact visual appearance:

Story	Screenshot
WithSxProps
WithSystemProps
WithStyleProps

The migration demonstrates the pattern for replacing styled-components usage with CSS modules while maintaining identical visual output. All styling properties (red text, blue background, Arial font, line-height, font-size, display flex) are preserved using CSS classes instead of runtime styled-components.

Technical Details

• Uses clsx for conditional class application as per project standards
• Added appropriate stylelint disable comments for demo-specific colors and fonts
• No changes to source components - migration is isolated to story files only
• All tests pass and build succeeds

Fixes #6575.

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Latest commit: 853cdd1

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