docs: add intro image to welcome page

[pixelflips]

Description

DSS-8: Added a hero image to the welcome documentation page to create a more engaging and professional introduction to Pine Design System.

Fixes DSS-8

Screenshots

Before	After

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)
• This change requires a documentation update

How Has This Been Tested?

• unit tests
• e2e tests
• accessibility tests
• tested manually (verified image displays correctly in Storybook documentation)

Test Configuration:

• Pine versions:
• OS:
• Browsers:
• Screen readers:
• Misc:

Checklist:

If not applicable, leave options unchecked.

• My code follows the style guidelines of this project
• I have performed a self-review of my 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 tests pass locally with my changes
• Design has QA'ed and approved this PR

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