Add a contributors section to the homepage

[AshutoshVJTI]

Context

Kardashev Labs is becoming an open-source project with room for contributors. The homepage should make that visible without turning into a recruiting page.

Scope

Add a small section near the GitHub CTA or footer that explains contributors are welcome and links to the org and CONTRIBUTING.md.

Acceptance criteria

• Section fits the existing visual style.
• Includes a link to https://github.com/kardashev-lab.
• Includes a short line like "Small PRs welcome."
• Looks good on mobile and desktop.

Helpful files

• app/page.tsx
• components/ToolsShowcase.tsx
• components/Footer.tsx