Fix incorrect README hero image

[sunjiajunsunjiajun]

Context

The README currently displays the hero image from assets/hero.png. We need to update the README image to correct mistakes in the current graphic.

Scope

• Review the current README image usage in README.md.
• Replace or regenerate assets/hero.png with a corrected version.
• Verify the README renders correctly after the image update.

Acceptance criteria

• The incorrect visual/text details in the README image are fixed.
• The image path in README.md remains valid.
• The updated README preview displays the corrected graphic without broken assets or layout issues.