fix: improve homepage contrast

[puneetdixit200]

Summary

• darken the highlighted "calmer" hero word in light mode so it clears WCAG contrast guidance
• keep the existing coral accent in dark mode, where it already has sufficient contrast
• force the footer "Zen Team" link to use the footer text color so the full "Made with ..." line stays readable in both themes

Closes #898.

Verification

• pnpm format
• pnpm lint
• pnpm typecheck
• pnpm build
• git diff --check
• rendered contrast check on http://127.0.0.1:3001/:
  • light hero highlight: 4.96:1
  • dark hero highlight: 5.77:1
  • light footer link: 11.87:1
  • dark footer link: 10.52:1

Used AI assistance to help draft and verify this change; I reviewed the diff and ran the checks above locally.

[taroj1205]

@puneetdixit200 thanks for the PR!
Could you please verify your commits?
I will discuss the color change with cheff.

[taroj1205]

Please verify your commits