Improve landing page clarity and mobile discovery

[Neofinal7]

What changed

• Added a clear iOS app CTA to the hero using the verified Gibwork App Store URL.
• Made the hero title a real semantic <h1> while preserving the sparkle presentation.
• Rewrote the FAQ copy to reflect email/social sign-in, escrowed rewards, and SPL-token payments.
• Added a wallet-start FAQ so the landing page no longer implies wallet-only onboarding.
• Added canonical, Open Graph, Twitter, and light/dark theme-color metadata.
• Added AI_DISCLOSURE.md as an explicit disclosure that this contribution was created with AI assistance.

Why

The landing page previously hid the shipped iOS app, used outdated wallet-only payment language, had no semantic page heading, and exposed only a single white theme-color. This PR makes the page more accurate and easier to discover without changing the product flow.

Verification

• npx tsc --noEmit — passed.
• npm run build — passed; production build compiled, generated all static pages, and completed Next.js type/lint checks.
• Targeted ESLint with next/core-web-vitals on every changed TypeScript file — passed with no errors or warnings. The repository-wide lint configuration is currently absent; when temporarily enabled, the only repository-wide error was the pre-existing unescaped apostrophe in components/logo-list.tsx.
• Browser behavior checks passed at 320, 375, 390, 414, 768, 1024, and 1440px widths: one <h1>, five FAQ controls, no horizontal overflow, and both hero CTAs remained inside the viewport.
• Exercised the new FAQ: it opens and exposes the new wallet guidance.
• Exercised the mobile menu: it opens and closes cleanly.
• Verified both external CTA destinations respond successfully: app.gib.work and the App Store URL.
• Captured desktop, mobile, and expanded-FAQ screenshots during local verification.

AI disclosure

This PR was created with AI assistance using OpenAI Codex. The implementation was reviewed and independently tested locally by the submitting contributor. See AI_DISCLOSURE.md.

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