Refresh landing page positioning and mobile app section

[laughlife]

Summary

This PR refreshes the landing page around Gibwork's current task-marketplace positioning and mobile app availability.

Changes include:

• Update hero and metadata copy to focus on bounties, task submissions, and USDC/Solana token payouts.
• Add an official iPhone app section with the App Store link and contributor-focused highlights.
• Add Mobile App links to desktop navigation, mobile menu, and footer quick links.
• Refresh task examples and FAQ copy to better explain bounties, tasks, approvals, and wallet payouts.

Related Gibwork task: b7c2a3c9-c412-4613-9cfb-d8a5f54d14b7 — Improve Gibwork Landing Page or Submit a GitHub Enhancement.

Verification

• npm run build
• Local Playwright render check at http://127.0.0.1:3210 for desktop, mobile viewport, mobile menu, and the new #mobile section.

Note: npm run lint currently opens Next.js' initial ESLint setup prompt because this repo does not have an ESLint config committed, so the production build was used for type/build validation.

[vercel]

Someone is attempting to deploy a commit to the gibwork Team on Vercel.

A member of the Team first needs to authorize it.

[laughlife]

Fresh verification from the PR branch: npm run build passes locally on commit e7dd98f8ea70e2c2d4dc387c0c76ea7d83282b62.

The only failing check shown on the PR is Vercel's fork deployment authorization prompt for the Gibwork team, not a build/type error in this branch.